View Category
Define an empty list
Assign the variable
"list" to a list with no elements
clojure
(list)
'()
cpp
Generic::List<String^>^ list = gcnew Generic::List<String^>();
std::list<std::string> list;
csharp
var list = new List<object>();
erlang
List = [],
fantom
list := [,]
fsharp
let list = []
let list = List.empty
let list = new Generic.List<string>()
let list = new Generic.LinkedList<string>()
groovy
list = []
// if a special kind of list is required
list = new LinkedList() // java style
LinkedList list = [] // statically typed
// using 'as' operator
list = [] as java.util.concurrent.CopyOnWriteArrayList
list = new LinkedList() // java style
LinkedList list = [] // statically typed
// using 'as' operator
list = [] as java.util.concurrent.CopyOnWriteArrayList
haskell
let list = []
java
List list = Collections.emptyList();
String[] list = {};
ocaml
let list = [];;
perl
@list = ();
python
list = []
ruby
list = []
list = Array.new
scala
val list = Nil
val list = List()
val list : List[String] = List()
Define a static list
Define the list
[One, Two, Three, Four, Five]
clojure
(def a '[One Two Three Four Five])
cpp
array<String^>^ input = {"One", "Two", "Three", "Four", "Five"};
Generic::List<String^>^ list = gcnew Generic::List<String^>((Generic::IEnumerable<String^>^) input);
Generic::List<String^>^ list = gcnew Generic::List<String^>((Generic::IEnumerable<String^>^) input);
Generic::List<String^>^ list = gcnew Generic::List<String^>();
list->Add("One");
list->Add("Two");
list->Add("Three");
list->Add("Four");
list->Add("Five");
list->Add("One");
list->Add("Two");
list->Add("Three");
list->Add("Four");
list->Add("Five");
std::string input[] = {"One", "Two", "Three", "Four", "Five"};
std::list<std::string> list(input, input + 5);
std::list<std::string> list(input, input + 5);
std::list<std::string> list;
list.push_back("One");
list.push_back("Two");
list.push_back("Three");
list.push_back("Four");
list.push_back("Five");
list.push_back("One");
list.push_back("Two");
list.push_back("Three");
list.push_back("Four");
list.push_back("Five");
list<string> lst = { "One", "Two", "Three", "Four", "Five" };
list<string> lst;
lst += "One", "Two", "Three", "Four", "Five";
lst += "One", "Two", "Three", "Four", "Five";
csharp
IList<string> list = new string[]{"One","Two","Three","Four","Five"};
erlang
List = [one, two, three, four, five],
List = ['One', 'Two', 'Three', 'Four', 'Five'],
fantom
list := ["One", "Two", "Three", "Four", "Five"]
fsharp
let list = ["One"; "Two"; "Three"; "Four"; "Five"]
let list = (new Generic.LinkedList<string>([|"One"; "Two"; "Three"; "Four"; "Five"|]))
let list = (new Generic.LinkedList<string>())
list.AddFirst("One") ; list.AddLast("Five") ; list.AddBefore(list.Find("Five"), "Four")
list.AddAfter(list.Find("One"), "Two") ; list.AddAfter(list.Find("Two"), "Three")
list.AddFirst("One") ; list.AddLast("Five") ; list.AddBefore(list.Find("Five"), "Four")
list.AddAfter(list.Find("One"), "Two") ; list.AddAfter(list.Find("Two"), "Three")
let list = (new Generic.List<string>())
[|"One"; "Two"; "Three"; "Four"; "Five"|] |> Array.iter (fun x -> list.Add(x))
[|"One"; "Two"; "Three"; "Four"; "Five"|] |> Array.iter (fun x -> list.Add(x))
groovy
list = ['One', 'Two', 'Three', 'Four', 'Five']
// other variations
List<String> numbers1 = ['One', 'Two', 'Three', 'Four', 'Five']
String[] numbers2 = ['One', 'Two', 'Three', 'Four', 'Five']
numbers3 = new LinkedList(['One', 'Two', 'Three', 'Four', 'Five'])
numbers4 = ['One', 'Two', 'Three', 'Four', 'Five'] as Stack // Groovy 1.6+
List<String> numbers1 = ['One', 'Two', 'Three', 'Four', 'Five']
String[] numbers2 = ['One', 'Two', 'Three', 'Four', 'Five']
numbers3 = new LinkedList(['One', 'Two', 'Three', 'Four', 'Five'])
numbers4 = ['One', 'Two', 'Three', 'Four', 'Five'] as Stack // Groovy 1.6+
haskell
let a = ["One", "Two", "Three", "Four", "Five"]
java
List<String> numbers = new ArrayList<String>();
Collections.addAll(numbers, "One", "Two", "Three", "Four", "Five");
Collections.addAll(numbers, "One", "Two", "Three", "Four", "Five");
List numbers = new ArrayList();
numbers.add("One");
numbers.add("Two");
numbers.add("Three");
numbers.add("Four");
numbers.add("Five");
numbers.add("One");
numbers.add("Two");
numbers.add("Three");
numbers.add("Four");
numbers.add("Five");
List numbers = Arrays.asList(new String[]{"One", "Two", "Three", "Four", "Five"});
String[] numbers = {"One", "Two", "Three", "Four", "Five"};
List numbers = new ArrayList(){{put("One"); put("Two"); put("Three"); put("Four"); put("Five"); }};
ocaml
let list = [ "One"; "Two"; "Three"; "Four"; "Five" ];;
perl
@list = qw(One Two Three Four Five);
@list = ('One', 'Two', 'Three', 'Four', 'Five');
python
list = ['One', 'Two', 'Three', 'Four', 'Five']
print list
print list
ruby
list = ['One', 'Two', 'Three', 'Four', 'Five']
list = %w(One Two Three Four Five)
scala
val list = "One" :: "Two" :: "Three" :: "Four" :: "Five" :: Nil
val list = List("One", "Two", "Three", "Four", "Five")
val list: List[String] = List("One", "Two", "Three", "Four", "Five")
Join the elements of a list, separated by commas
Given the list
[Apple, Banana, Carrot] produce "Apple, Banana, Carrot"
clojure
(apply str (interpose ", " '("Apple" "Banana" "Carrot")))
cpp
String^ result = String::Join(L", ", fruit->ToArray());
string fruits[] = {"Apple", "Banana", "Carrot"};
string result = boost::algorithm::join(fruits, ", ");
string result = boost::algorithm::join(fruits, ", ");
csharp
using System.Collections.Generic;
public class JoinEach {
public static void Main() {
var list = new List<string>() {"Apple", "Banana", "Carrot"};
System.Console.WriteLine( string.Join(", ", list.ToArray()) );
}
}
public class JoinEach {
public static void Main() {
var list = new List<string>() {"Apple", "Banana", "Carrot"};
System.Console.WriteLine( string.Join(", ", list.ToArray()) );
}
}
erlang
Result = string:join(Fruit, ", "),
Result = lists:foldl(fun (E, Acc) -> Acc ++ ", " ++ E end, hd(Fruit), tl(Fruit)),
Result = lists:flatten([ hd(Fruit) | [ ", " ++ X || X <- tl(Fruit)]]).
fantom
["Apple", "Banana", "Carrot"].join(", ")
fsharp
let result = String.Join(", ", [|"Apple"; "Banana"; "Carrot"|])
let result = (List.fold_left (fun acc item -> acc ^ (", " ^ item)) (List.hd fruit) (List.tl fruit))
let result = (List.fold_left (fun (acc : StringBuilder) (item : string) -> acc.Append(", ").Append(item)) (new StringBuilder(List.hd fruit)) (List.tl fruit)).ToString()
groovy
string = fruit.join(', ')
string = fruit.toString()[1..-2]
haskell
import Data.List
let join = intercalate ", " ["Apple", "Banana", "Carrot"]
let join = intercalate ", " ["Apple", "Banana", "Carrot"]
java
StringBuffer sb = new StringBuffer();
for (Iterator it = fruit.iterator(); it.hasNext();) {
sb.append(it.next());
if (it.hasNext()) {
sb.append(", ");
}
}
String result = sb.toString();
for (Iterator it = fruit.iterator(); it.hasNext();) {
sb.append(it.next());
if (it.hasNext()) {
sb.append(", ");
}
}
String result = sb.toString();
StringBuilder sb = new StringBuilder(fruit.get(0));
for (String item : fruit.subList(1, fruit.size())) sb.append(", ").append(item);
String result = sb.toString();
for (String item : fruit.subList(1, fruit.size())) sb.append(", ").append(item);
String result = sb.toString();
String result = StringUtils.join(fruit, ", ");
ocaml
let () =
let lst = ["Apple"; "Banana"; "Carrot"] in
let str = String.concat ", " lst in
print_endline str
let lst = ["Apple"; "Banana"; "Carrot"] in
let str = String.concat ", " lst in
print_endline str
perl
print join ', ', qw(Apple Banana Carrot);
# Longer and less efficient than join(), but illustrates
# Perl's foreach operator, which can be useful for
# less trivial problems with lists
@list = ('Apple', 'Banana', 'Carrot');
foreach $fruit (@list) {
print "$fruit,";
}
print "\n";
# Perl's foreach operator, which can be useful for
# less trivial problems with lists
@list = ('Apple', 'Banana', 'Carrot');
foreach $fruit (@list) {
print "$fruit,";
}
print "\n";
my @a = qw/Apple Banana Carrot/;
{
local $, = ", ";
print @a
}
print "\n";
{
local $, = ", ";
print @a
}
print "\n";
my @a = qw/Apple Banana Carrot/;
{
local $" = ", ";
print "@a\n";
}
{
local $" = ", ";
print "@a\n";
}
python
print ", ".join(['Apple', 'Banana', 'Carrot'])
ruby
string = fruit.join(', ')
scala
val result =
((fruit.tail foldLeft (new StringBuilder(fruit.head))) {(acc, e) => acc.append(", ").append(e)}).toString
((fruit.tail foldLeft (new StringBuilder(fruit.head))) {(acc, e) => acc.append(", ").append(e)}).toString
val result = fruit.mkString(",")
val fruit = List[String]("Apple", "Banana", "Carrot")
println(fruit.mkString(", "))
println(fruit.mkString(", "))
Join the elements of a list, in correct english
Create a function join that takes a List and produces a string containing an english language concatenation of the list. It should work with the following examples:
join(
join(
join(
join(
join(
[Apple, Banana, Carrot]) = "Apple, Banana, and Carrot"
join(
[One, Two]) = "One and Two"
join(
[Lonely]) = "Lonely"
join(
[]) = ""
clojure
(defn join [lst]
(cond
(= (count lst) 0) ""
(= (count lst) 1) (first lst)
(= (count lst) 2) (str (first lst) " and " (second lst))
(> (count lst) 2) (loop [lst lst sb (StringBuilder.)]
(if (empty? lst)
(.toString sb)
(recur (rest lst) (.append sb (cond
(> (count lst) 2) (str (first lst) ", ")
(> (count lst) 1) (str (first lst) ", and ")
(= (count lst) 1) (str (first lst)))))))))
(cond
(= (count lst) 0) ""
(= (count lst) 1) (first lst)
(= (count lst) 2) (str (first lst) " and " (second lst))
(> (count lst) 2) (loop [lst lst sb (StringBuilder.)]
(if (empty? lst)
(.toString sb)
(recur (rest lst) (.append sb (cond
(> (count lst) 2) (str (first lst) ", ")
(> (count lst) 1) (str (first lst) ", and ")
(= (count lst) 1) (str (first lst)))))))))
(defn join
([lst]
(join lst false))
([lst is-long]
(condp = (count lst)
0 ""
1 (first lst)
2 (str (first lst) (if is-long ",") " and " (second lst))
(str (first lst) ", " (join (rest lst) true)))))
([lst]
(join lst false))
([lst is-long]
(condp = (count lst)
0 ""
1 (first lst)
2 (str (first lst) (if is-long ",") " and " (second lst))
(str (first lst) ", " (join (rest lst) true)))))
cpp
Console::WriteLine(join(fruit));
string join(const vector<string> &s, int b=0)
{
switch (s.size() - b)
{
case 0: return "";
case 1: return s[b];
case 2: return s[b] + (s.size() > 2 ? "," : "") + " and " + s[b+1];
default: return s[b] + ", " + join(s, b+1);
}
}
{
switch (s.size() - b)
{
case 0: return "";
case 1: return s[b];
case 2: return s[b] + (s.size() > 2 ? "," : "") + " and " + s[b+1];
default: return s[b] + ", " + join(s, b+1);
}
}
csharp
using System.Collections.Generic;
using System.Linq;
public class CSharpListToEnglishList {
public string JoinAsEnglishList (List<string> words) {
switch (words.Count) {
case 0: return "";
case 1: return words[0];
case 2: return string.Format("{0} and {1}", words.ToArray());
default:
return JoinAsEnglishList( new List<string>() {
string.Join(", ", words.Take(words.Count - 1).ToArray()) + ",",
words.Last()
});
}
}
// Driver...
public static void Main() {
var joiner = new CSharpListToEnglishList();
System.Console.WriteLine(
joiner.JoinAsEnglishList(new List<string>() { "Apple", "Banana", "Carrot", "Orange" }) );
System.Console.WriteLine(
joiner.JoinAsEnglishList(new List<string>() { "Apple", "Banana", "Carrot" }) );
System.Console.WriteLine(
joiner.JoinAsEnglishList(new List<string>() { "One", "Two" }) );
System.Console.WriteLine(
joiner.JoinAsEnglishList(new List<string>() { "Lonely" }) );
System.Console.WriteLine(
joiner.JoinAsEnglishList(new List<string>()) );
}
}
using System.Linq;
public class CSharpListToEnglishList {
public string JoinAsEnglishList (List<string> words) {
switch (words.Count) {
case 0: return "";
case 1: return words[0];
case 2: return string.Format("{0} and {1}", words.ToArray());
default:
return JoinAsEnglishList( new List<string>() {
string.Join(", ", words.Take(words.Count - 1).ToArray()) + ",",
words.Last()
});
}
}
// Driver...
public static void Main() {
var joiner = new CSharpListToEnglishList();
System.Console.WriteLine(
joiner.JoinAsEnglishList(new List<string>() { "Apple", "Banana", "Carrot", "Orange" }) );
System.Console.WriteLine(
joiner.JoinAsEnglishList(new List<string>() { "Apple", "Banana", "Carrot" }) );
System.Console.WriteLine(
joiner.JoinAsEnglishList(new List<string>() { "One", "Two" }) );
System.Console.WriteLine(
joiner.JoinAsEnglishList(new List<string>() { "Lonely" }) );
System.Console.WriteLine(
joiner.JoinAsEnglishList(new List<string>()) );
}
}
erlang
io:format("~s~n", [join(Fruit)]).
% ------
join([]) -> "";
join([W|Ws]) -> join(Ws, W).
join([], S) -> S;
join([W], S) -> join([], S ++ " and " ++ W);
join([W|Ws], S) -> join(Ws, S ++ ", " ++ W).
% ------
join([]) -> "";
join([W|Ws]) -> join(Ws, W).
join([], S) -> S;
join([W], S) -> join([], S ++ " and " ++ W);
join([W|Ws], S) -> join(Ws, S ++ ", " ++ W).
%% According to the reference manual, "string is not a data type in Erlang."
%% Instead it has lists of integers. But I/O functions in general accept
%% IO lists, where an IO list is either a list of IO lists or an integer.
%% This gives you O(1) string concatenation.
-module(commalist).
-export([join/1]).
join([]) -> "";
join([W]) -> W;
join([W1, W2]) -> [W1, " and ", W2];
join([W1, W2, W3]) -> [W1, ", ", W2, ", and ", W3];
join([W1|Ws]) -> [W1, ", ", join(Ws)].
%% Instead it has lists of integers. But I/O functions in general accept
%% IO lists, where an IO list is either a list of IO lists or an integer.
%% This gives you O(1) string concatenation.
-module(commalist).
-export([join/1]).
join([]) -> "";
join([W]) -> W;
join([W1, W2]) -> [W1, " and ", W2];
join([W1, W2, W3]) -> [W1, ", ", W2, ", and ", W3];
join([W1|Ws]) -> [W1, ", ", join(Ws)].
fantom
join := |List list -> Str|
{
switch(list.size)
{
case 0: return ""
case 1: return list[0]
case 2: return list.join(" and ")
default: return list[0..-2].join(", ") + ", and " + list[-1]
}
}
echo(join(["Apple", "Banana", "Carrot"]))
echo(join(["One", "Two"]))
echo(join(["Lonely"]))
echo(join([,]))
{
switch(list.size)
{
case 0: return ""
case 1: return list[0]
case 2: return list.join(" and ")
default: return list[0..-2].join(", ") + ", and " + list[-1]
}
}
echo(join(["Apple", "Banana", "Carrot"]))
echo(join(["One", "Two"]))
echo(join(["Lonely"]))
echo(join([,]))
fsharp
let join list =
let rec join' list' s =
match list' with
| [] -> s
| [w] -> join' [] (s ^ " and " ^ w)
| w :: ws -> join' ws (s ^ ", " ^ w)
match list with
| [] -> ""
| w :: ws -> join' ws w
// ------
printfn "%s" (join fruit)
let rec join' list' s =
match list' with
| [] -> s
| [w] -> join' [] (s ^ " and " ^ w)
| w :: ws -> join' ws (s ^ ", " ^ w)
match list with
| [] -> ""
| w :: ws -> join' ws w
// ------
printfn "%s" (join fruit)
groovy
def join(list) {
if (!list) return ''
switch(list.size()) {
case 1:
return list[0]
case 2:
return list.join(' and ')
default:
return list[0..-2].join(', ') + ', and ' + list[-1]
}
}
if (!list) return ''
switch(list.size()) {
case 1:
return list[0]
case 2:
return list.join(' and ')
default:
return list[0..-2].join(', ') + ', and ' + list[-1]
}
}
ArrayList.metaClass.joinEng = { ->
def closureMap = [0: { -> delegate.join(' and ')}, 1 : {-> delegate.join(' and ')}].withDefault { k -> { -> delegate[0..-2].join(', ') + ', and ' + delegate[-1] } }
if (delegate.size()) closureMap[delegate.size()-1].call()
else ""
}
assert ["a"].joinEng() == "a"
assert ["a", "b"].joinEng() == "a and b"
assert ["a", "b", "c"].joinEng() == "a, b, and c"
assert [].joinEng() == ""
def closureMap = [0: { -> delegate.join(' and ')}, 1 : {-> delegate.join(' and ')}].withDefault { k -> { -> delegate[0..-2].join(', ') + ', and ' + delegate[-1] } }
if (delegate.size()) closureMap[delegate.size()-1].call()
else ""
}
assert ["a"].joinEng() == "a"
assert ["a", "b"].joinEng() == "a and b"
assert ["a", "b", "c"].joinEng() == "a, b, and c"
assert [].joinEng() == ""
haskell
join [] = ""
join [x] = x
join [x,y] = x ++ " and " ++ y
join [x,y,z] = x ++ ", " ++ y ++ ", and " ++ z
join (x:xs) = x ++ ", " ++ join xs
join [x] = x
join [x,y] = x ++ " and " ++ y
join [x,y,z] = x ++ ", " ++ y ++ ", and " ++ z
join (x:xs) = x ++ ", " ++ join xs
java
private String join(List elements) {
if (elements == null || elements.size() == 0) {
return "";
} else if (elements.size() == 1) {
return elements.get(0).toString();
} else if (elements.size() == 2) {
return elements.get(0) + " and " + elements.get(1);
}
StringBuffer sb = new StringBuffer();
for (Iterator it = elements.iterator(); it.hasNext();) {
String next = (String) it.next();
if (sb.length() > 0) {
if (it.hasNext()) {
sb.append(", ");
} else {
sb.append(", and ");
}
}
sb.append(next);
}
return sb.toString();
}
if (elements == null || elements.size() == 0) {
return "";
} else if (elements.size() == 1) {
return elements.get(0).toString();
} else if (elements.size() == 2) {
return elements.get(0) + " and " + elements.get(1);
}
StringBuffer sb = new StringBuffer();
for (Iterator it = elements.iterator(); it.hasNext();) {
String next = (String) it.next();
if (sb.length() > 0) {
if (it.hasNext()) {
sb.append(", ");
} else {
sb.append(", and ");
}
}
sb.append(next);
}
return sb.toString();
}
System.out.println(join(fruit));
ocaml
let join list =
let rec join' list acc =
match list with
| [] -> ""
| [single] -> single
| one::[two] ->
if acc = "" then one ^ " and " ^ two
else acc ^ one ^ ", and " ^ two
| first::others -> join' others (acc ^ first ^ ", ")
in
join' list ""
let rec join' list acc =
match list with
| [] -> ""
| [single] -> single
| one::[two] ->
if acc = "" then one ^ " and " ^ two
else acc ^ one ^ ", and " ^ two
| first::others -> join' others (acc ^ first ^ ", ")
in
join' list ""
perl
sub myjoin {
$_ = join ', ', @_;
s/, ([^,]+)$/ and $1/;
return $_;
}
# Note: I don't think this meets the spec --Geoff
$_ = join ', ', @_;
s/, ([^,]+)$/ and $1/;
return $_;
}
# Note: I don't think this meets the spec --Geoff
sub myjoin {
if ($#_ < 2) {
return join ' and ', @_;
} else {
return join(', ', @_[0..$#_-1]) . ' and ' . $_[-1];
}
}
# Note: I don't think this meets the spec --Geoff
if ($#_ < 2) {
return join ' and ', @_;
} else {
return join(', ', @_[0..$#_-1]) . ' and ' . $_[-1];
}
}
# Note: I don't think this meets the spec --Geoff
# Previous "myjoin()" responses don't meet the spec of including
# the final comma before the "and" if the list has more than
# two elements...this is one way to meet that spec...it may
# not be the most efficient...
sub AnotherMyJoin {
my @list = @_;
if ($#list == -1) {return}
elsif ($#list == 0) {return $list[0]}
elsif ($#list == 1) {return $list[0].' and '.$list[1]}
else {
return join(", ", @list[0..$#list - 1]) . ', and '. $list[$#list];
}
}
# the final comma before the "and" if the list has more than
# two elements...this is one way to meet that spec...it may
# not be the most efficient...
sub AnotherMyJoin {
my @list = @_;
if ($#list == -1) {return}
elsif ($#list == 0) {return $list[0]}
elsif ($#list == 1) {return $list[0].' and '.$list[1]}
else {
return join(", ", @list[0..$#list - 1]) . ', and '. $list[$#list];
}
}
# This is the long way, but it's kind of fun
# It illustrates the use of Perl's reverse()
# operator to work our way through the list
# elements backwards...I wrote this one before
# getting smart and looking at some of the other
# algorithms from the other languages. Still,
# it is only 12 lines of code vs 9 for my other
# solution if you disregard the comments.
sub myjoin {
my @list = reverse(@_); # Reverse original order of elements
my $retval;
# Make our exit here if we were passed an empty list
if ($#list == -1) {return}
# Loop through reversed elements in end-to-start order
for (0..$#list) {
# Add the reversed form of each element plus a space char
$retval .= reverse($list[$_]).' ';
# Add 'and' to lists with two or more elements
# placing it in between final and 'next to final'
$retval .= "dna " if ($#list > 0 and $_== 0);
# Add ',' to each element as long as there are more
# than two elements and the current element isn't the
# final element
$retval .= "," if ($#list > 1 and $_ != $#list);
}
# Remove what will end up as an extraneous leading space
chop($retval);
# Done looping, now reverse things back into correct order and return
$retval = reverse($retval);
return($retval);
}
# It illustrates the use of Perl's reverse()
# operator to work our way through the list
# elements backwards...I wrote this one before
# getting smart and looking at some of the other
# algorithms from the other languages. Still,
# it is only 12 lines of code vs 9 for my other
# solution if you disregard the comments.
sub myjoin {
my @list = reverse(@_); # Reverse original order of elements
my $retval;
# Make our exit here if we were passed an empty list
if ($#list == -1) {return}
# Loop through reversed elements in end-to-start order
for (0..$#list) {
# Add the reversed form of each element plus a space char
$retval .= reverse($list[$_]).' ';
# Add 'and' to lists with two or more elements
# placing it in between final and 'next to final'
$retval .= "dna " if ($#list > 0 and $_== 0);
# Add ',' to each element as long as there are more
# than two elements and the current element isn't the
# final element
$retval .= "," if ($#list > 1 and $_ != $#list);
}
# Remove what will end up as an extraneous leading space
chop($retval);
# Done looping, now reverse things back into correct order and return
$retval = reverse($retval);
return($retval);
}
# Yes, this doesn't meet the spec, the spec is flawed
# the serial comma (Oxford comma) is not required in a list
sub english_join {
return join(', ', @_[0..$#_-1])
. ($#_ ? ' and ' : '' )
. $_[-1];
}
# the serial comma (Oxford comma) is not required in a list
sub english_join {
return join(', ', @_[0..$#_-1])
. ($#_ ? ' and ' : '' )
. $_[-1];
}
python
def join(*x):
if len(x) <= 2:
return ' and '.join(x)
else:
return ', '.join(x[:-1] + ('and ' + x[-1],))
if __name__ == "__main__":
assert join("Apple", "Banana", "Carrot") == "Apple, Banana, and Carrot"
assert join("One", "Two") == "One and Two"
assert join("Lonely") == "Lonely"
assert join(*[]) == ""
if len(x) <= 2:
return ' and '.join(x)
else:
return ', '.join(x[:-1] + ('and ' + x[-1],))
if __name__ == "__main__":
assert join("Apple", "Banana", "Carrot") == "Apple, Banana, and Carrot"
assert join("One", "Two") == "One and Two"
assert join("Lonely") == "Lonely"
assert join(*[]) == ""
ruby
def join(arr)
return '' if not arr
case arr.size
when 0 then ''
when 1 then arr[0]
when 2 then arr.join(' and ')
else arr[0..-2].join(', ') + ', and ' + arr[-1]
end
end
return '' if not arr
case arr.size
when 0 then ''
when 1 then arr[0]
when 2 then arr.join(' and ')
else arr[0..-2].join(', ') + ', and ' + arr[-1]
end
end
scala
def join(list : List[String]) : String = list match {
case List() => ""
case List(x) => x
case List(x,y) => x + " and " + y
case List(x,y,z) => x + ", " + y + ", and " + z
case _ => list(0) + ", " + join(list.tail)
}
case List() => ""
case List(x) => x
case List(x,y) => x + " and " + y
case List(x,y,z) => x + ", " + y + ", and " + z
case _ => list(0) + ", " + join(list.tail)
}
def join(list : List[String]) : String = list match {
case List() => ""
case List(x) => x
case List(x,y) => x + " and " + y
case List(x,y,z) => x + ", " + y + ", and " + z
case x::xs => x + ", " + join(xs)
}
case List() => ""
case List(x) => x
case List(x,y) => x + " and " + y
case List(x,y,z) => x + ", " + y + ", and " + z
case x::xs => x + ", " + join(xs)
}
def join[T](list : List[T]) = list match {
case xs if xs.size < 3 => xs.mkString(" and ")
case xs => xs.init.mkString(", ") + ", and " + xs.last
}
case xs if xs.size < 3 => xs.mkString(" and ")
case xs => xs.init.mkString(", ") + ", and " + xs.last
}
Produce the combinations from two lists
Given two lists, produce the list of tuples formed by taking the combinations from the individual lists. E.g. given the letters
["a", "b", "c"] and the numbers [4, 5], produce the list: [["a", 4], ["b", 4], ["c", 4], ["a", 5], ["b", 5], ["c", 5]]
clojure
(defn combine [lst1 lst2]
(mapcat (fn [x] (map #(list % x) lst1)) lst2))
(mapcat (fn [x] (map #(list % x) lst1)) lst2))
(mapcat (fn [x] (map #(list % x) ["a", "b", "c"])) [4, 5])
cpp
Specialized::StringCollection^ combinations = gcnew Specialized::StringCollection;
for each(int number in numbers)
for each(String^ letter in letters)
combinations->Add(makeCombo(letter, number));
for each(int number in numbers)
for each(String^ letter in letters)
combinations->Add(makeCombo(letter, number));
string letters[] = { "a", "b", "c" };
int numbers[] = { 4, 5 };
list<pair<string,int> > combo;
for (int n = 0; n < sizeof numbers / sizeof *numbers; n++)
for (int l = 0; l < sizeof letters / sizeof *letters; l++)
combo.push_back(make_pair(letters[l], numbers[n]));
cout << combo << endl;
int numbers[] = { 4, 5 };
list<pair<string,int> > combo;
for (int n = 0; n < sizeof numbers / sizeof *numbers; n++)
for (int l = 0; l < sizeof letters / sizeof *letters; l++)
combo.push_back(make_pair(letters[l], numbers[n]));
cout << combo << endl;
csharp
using System.Collections.Generic;
public class ListCombiner {
public static void Main() {
var letters = new List<char>() { 'a', 'b', 'c' };
var numbers = new List<int>() { 1, 2, 3 };
// result is a list that contaings lists of objects
var result = new List<List<object>>();
foreach (var l in letters) {
foreach (var n in numbers) {
result.Add(new List<object>() { l, n });
}
}
}
}
public class ListCombiner {
public static void Main() {
var letters = new List<char>() { 'a', 'b', 'c' };
var numbers = new List<int>() { 1, 2, 3 };
// result is a list that contaings lists of objects
var result = new List<List<object>>();
foreach (var l in letters) {
foreach (var n in numbers) {
result.Add(new List<object>() { l, n });
}
}
}
}
erlang
Combinations =
lists:foldl(fun (Number, Acc) -> Acc ++ lists:map(fun (Letter) -> {Letter, Number} end, Letters) end, [], Numbers),
lists:foldl(fun (Number, Acc) -> Acc ++ lists:map(fun (Letter) -> {Letter, Number} end, Letters) end, [], Numbers),
Combinations = lists:keysort(2, sofs:to_external(sofs:product(sofs:set(Letters), sofs:set(Numbers))))
[[A, B] || A <- ["a", "b", "c"], B <- [4, 5]].
fantom
[4,5].each |Int i| { ["a","b","c"].each |Str s| { r.add([i,s]) } }
fsharp
let combinations = (List.fold_left (fun acc number -> acc @ (List.map (fun letter -> (letter, number)) letters)) [] numbers)
let combinations aa bb =
aa
|> List.map (fun a -> bb |> List.map (fun b -> (a, b)))
|> List.concat
aa
|> List.map (fun a -> bb |> List.map (fun b -> (a, b)))
|> List.concat
groovy
letters = ['a', 'b', 'c']
numbers = [4, 5]
combos = [letters, numbers].combinations()
numbers = [4, 5]
combos = [letters, numbers].combinations()
haskell
comb :: [(String, Int)]
comb = do
b <- [4,5]
a <- ["a","b","c"]
return (a,b)
main = mapM_ print comb
comb = do
b <- [4,5]
a <- ["a","b","c"]
return (a,b)
main = mapM_ print comb
comb :: [(String, Int)]
comb = [(a, b) | b <- [4,5], a <- ["a","b","c"]]
main = print comb
comb = [(a, b) | b <- [4,5], a <- ["a","b","c"]]
main = print comb
java
List<String> combinations = new ArrayList<String>();
for (int number : numbers)
for (String letter : letters)
combinations.add(letter + ":" + Integer.toString(number));
for (int number : numbers)
for (String letter : letters)
combinations.add(letter + ":" + Integer.toString(number));
SortedSet<AbstractMap.SimpleImmutableEntry<String, Integer> > combinations =
new TreeSet<AbstractMap.SimpleImmutableEntry<String, Integer> >(new CombinationComparator());
for (int number : numbers)
for (String letter : letters)
combinations.add(new AbstractMap.SimpleImmutableEntry<String, Integer>(letter, Integer.valueOf(number)));
new TreeSet<AbstractMap.SimpleImmutableEntry<String, Integer> >(new CombinationComparator());
for (int number : numbers)
for (String letter : letters)
combinations.add(new AbstractMap.SimpleImmutableEntry<String, Integer>(letter, Integer.valueOf(number)));
ocaml
let combinations =
let l1 = ["a"; "b"; "c"]
and l2 = [4; 5] in
List.rev (
List.fold_left (fun acc y ->
List.fold_left (fun acc2 x ->
(x, y)::acc2
) acc l1
) [] l2
)
let l1 = ["a"; "b"; "c"]
and l2 = [4; 5] in
List.rev (
List.fold_left (fun acc y ->
List.fold_left (fun acc2 x ->
(x, y)::acc2
) acc l1
) [] l2
)
perl
@letters = qw(a b c);
@numbers = (4, 5);
@list = map { $number=$_; map [$_, $number], @letters; } @numbers;
@numbers = (4, 5);
@list = map { $number=$_; map [$_, $number], @letters; } @numbers;
@letters = qw(a b c);
@numbers = (4, 5);
for $number (@numbers) {
for $letter (@letters) {
push @list, [$letter, $number];
}
}
@numbers = (4, 5);
for $number (@numbers) {
for $letter (@letters) {
push @list, [$letter, $number];
}
}
python
[(x, y) for y in [1,2] for x in ['a','b','c']]
import itertools
[x for x in itertools.product(["a", "b", "c"], [4, 5])]
[x for x in itertools.product(["a", "b", "c"], [4, 5])]
ruby
common = [] ; [4, 5].each {|n| ['a', 'b', 'c'].each {|l| common << [l, n]}}
scala
val combinations =
(numbers foldLeft List[Pair[String, Int]]()) { (acc : List[Pair[String, Int]], number : Int) =>
acc ::: (letters map { (letter : String) => Pair(letter : String, number : Int) }) }
(numbers foldLeft List[Pair[String, Int]]()) { (acc : List[Pair[String, Int]], number : Int) =>
acc ::: (letters map { (letter : String) => Pair(letter : String, number : Int) }) }
def product(set1 : List[_], set2 : List[_]) : List[Pair[_, _]] =
{
val p = new mutable.ArrayBuffer[Pair[_, _]]()
for (e1 <- set1) for (e2 <- set2) p += Pair(e1, e2)
p.toList
}
// ------
val combinations =
product(numbers, letters) map { (c) => c match { case Pair(number, letter) => Pair(letter, number) } }
{
val p = new mutable.ArrayBuffer[Pair[_, _]]()
for (e1 <- set1) for (e2 <- set2) p += Pair(e1, e2)
p.toList
}
// ------
val combinations =
product(numbers, letters) map { (c) => c match { case Pair(number, letter) => Pair(letter, number) } }
val letters = List('a', 'b', 'c')
val numbers = List(4, 5)
for { l <- letters; n <- numbers } yield (l,n)
val numbers = List(4, 5)
for { l <- letters; n <- numbers } yield (l,n)
From a List Produce a List of Duplicate Entries
Taking a list:
Write the code to produce a list of duplicates in the list:
["andrew", "bob", "chris", "bob"]
Write the code to produce a list of duplicates in the list:
["bob"]
clojure
(->> '("andrew" "bob" "chris" "bob")
(group-by identity)
(filter #(> (count (second %)) 1))
(map first))
(group-by identity)
(filter #(> (count (second %)) 1))
(map first))
cpp
vector<string> lst = { "andrew", "bob", "chris", "bob" };
vector<string> lst_no_dups;
vector<string> tmp;
vector<string> dups;
sort(lst.begin(), lst.end());
unique_copy(lst.begin(), lst.end(), back_inserter(lst_no_dups));
set_difference(lst.begin(), lst.end(),
lst_no_dups.begin(), lst_no_dups.end(),
back_inserter(tmp));
unique_copy(tmp.begin(), tmp.end(), back_inserter(dups));
cout << dups << endl;
vector<string> lst_no_dups;
vector<string> tmp;
vector<string> dups;
sort(lst.begin(), lst.end());
unique_copy(lst.begin(), lst.end(), back_inserter(lst_no_dups));
set_difference(lst.begin(), lst.end(),
lst_no_dups.begin(), lst_no_dups.end(),
back_inserter(tmp));
unique_copy(tmp.begin(), tmp.end(), back_inserter(dups));
cout << dups << endl;
list<string> lst = { "andrew", "bob", "chris", "bob" };
map<string,int> num_identical;
list<string> dups;
for (auto &s: lst)
num_identical[s]++;
for (auto &n: num_identical)
if (n.second > 1)
dups.push_back(n.first);
cout << dups << endl;
map<string,int> num_identical;
list<string> dups;
for (auto &s: lst)
num_identical[s]++;
for (auto &n: num_identical)
if (n.second > 1)
dups.push_back(n.first);
cout << dups << endl;
csharp
List<String> values = new List<string> {"andrew", "bob", "chris", "bob"};
var duplicates = values
.GroupBy(i => i)
.Where(j => j.Count() > 1)
.Select(s => s.Key);
foreach (var duplicate in duplicates)
{
Console.WriteLine(duplicate);
}
var duplicates = values
.GroupBy(i => i)
.Where(j => j.Count() > 1)
.Select(s => s.Key);
foreach (var duplicate in duplicates)
{
Console.WriteLine(duplicate);
}
erlang
{_, Result} = lists:foldl(
fun(X, {Uniq, Dupl}) -> case lists:member(X, Uniq) of
true -> {Uniq,[X | Dupl]};
_ -> {[X | Uniq], Dupl}
end
end,
{[], []},
List),
fun(X, {Uniq, Dupl}) -> case lists:member(X, Uniq) of
true -> {Uniq,[X | Dupl]};
_ -> {[X | Uniq], Dupl}
end
end,
{[], []},
List),
Fun = fun
([X | Xs], F) -> case lists:member(X, Xs) of
true -> [X | F(Xs, F)];
_ -> F(Xs, F)
end;
([], _) -> []
end,
Result = Fun(List, Fun).
([X | Xs], F) -> case lists:member(X, Xs) of
true -> [X | F(Xs, F)];
_ -> F(Xs, F)
end;
([], _) -> []
end,
Result = Fun(List, Fun).
fantom
nameCounts := Str:Int[:] { def = 0 }
["andrew", "bob", "chris", "bob"].each |Str v| { nameCounts[v]++ }
results := nameCounts.findAll |Int v, Str k->Bool| { v > 1 }.keys
echo(results.join(","))
["andrew", "bob", "chris", "bob"].each |Str v| { nameCounts[v]++ }
results := nameCounts.findAll |Int v, Str k->Bool| { v > 1 }.keys
echo(results.join(","))
fsharp
["andrew"; "bob"; "chris"; "bob"]
|> Seq.countBy id
|> Seq.filter (fun (k,n) -> n > 1)
|> Seq.map fst
|> Seq.toList
|> Seq.countBy id
|> Seq.filter (fun (k,n) -> n > 1)
|> Seq.map fst
|> Seq.toList
groovy
def input = ["andrew", "bob", "chris", "bob"]
def output = input.findAll{input.count(it)>1}.unique()
assert output == ["bob"]
def output = input.findAll{input.count(it)>1}.unique()
assert output == ["bob"]
haskell
import Data.List
input = ["andrew", "bob", "chris", "bob"]
output = [ head l | l <- group (sort input), length l > 1]
input = ["andrew", "bob", "chris", "bob"]
output = [ head l | l <- group (sort input), length l > 1]
java
List listOfDuplicates = new ArrayList(Arrays.asList(new String[]{"andrew", "bob", "chris", "bob"}));
Set set = new HashSet(listOfDuplicates);
for (Object element : set)
listOfDuplicates.remove(element);
Set set = new HashSet(listOfDuplicates);
for (Object element : set)
listOfDuplicates.remove(element);
ocaml
let rem v lst =
let rec aux acc = function
| [] -> List.rev acc
| x::xs ->
if compare v x = 0
then aux acc xs
else aux (x::acc) xs
in
aux [] lst
(** in case of a match, returns a list with the duplicate(s) removed *)
let rec mem_rem v lst =
let rec aux acc = function
| [] -> None
| x::xs ->
if compare v x = 0
then Some(List.rev_append acc (rem v xs))
else aux (x::acc) xs
in
aux [] lst
let duplicates lst =
let rec aux acc = function
| [] -> List.rev acc
| x::xs ->
match mem_rem x xs with
| Some ret -> aux (x::acc) ret
| None -> aux acc xs
in
aux [] lst
let () =
let lst = ["andrew"; "bob"; "chris"; "bob"; "mike"; "peter"; "bob"] in
let dup = duplicates lst in
List.iter print_endline dup
let rec aux acc = function
| [] -> List.rev acc
| x::xs ->
if compare v x = 0
then aux acc xs
else aux (x::acc) xs
in
aux [] lst
(** in case of a match, returns a list with the duplicate(s) removed *)
let rec mem_rem v lst =
let rec aux acc = function
| [] -> None
| x::xs ->
if compare v x = 0
then Some(List.rev_append acc (rem v xs))
else aux (x::acc) xs
in
aux [] lst
let duplicates lst =
let rec aux acc = function
| [] -> List.rev acc
| x::xs ->
match mem_rem x xs with
| Some ret -> aux (x::acc) ret
| None -> aux acc xs
in
aux [] lst
let () =
let lst = ["andrew"; "bob"; "chris"; "bob"; "mike"; "peter"; "bob"] in
let dup = duplicates lst in
List.iter print_endline dup
(* Using standard (functorized) sets *)
module SetTools(ASet: Set.S) =
struct
let find_duplicates l =
let rec aux l seen acc =
match l with
| [] -> acc
| h :: q ->
if ASet.mem h seen then
aux q seen (h :: acc)
else
aux q (ASet.add h seen) acc in
aux l (ASet.empty) []
end
module StringSet = Set.Make(String)
module StringSetTools = SetTools(StringSet)
StringSetTools.find_duplicates ["andrew"; "bob"; "chris"; "bob"];;
module SetTools(ASet: Set.S) =
struct
let find_duplicates l =
let rec aux l seen acc =
match l with
| [] -> acc
| h :: q ->
if ASet.mem h seen then
aux q seen (h :: acc)
else
aux q (ASet.add h seen) acc in
aux l (ASet.empty) []
end
module StringSet = Set.Make(String)
module StringSetTools = SetTools(StringSet)
StringSetTools.find_duplicates ["andrew"; "bob"; "chris"; "bob"];;
perl
my @input = ("andrew", "bob", "chris", "bob", "bob");
my %input_count;
my @output = grep { $input_count{$_}++; $input_count{$_} == 2 } @input;
my %input_count;
my @output = grep { $input_count{$_}++; $input_count{$_} == 2 } @input;
python
import itertools
input = ["andrew", "bob", "chris", "bob"]
input.sort()
output = [k for k, g in itertools.groupby(input, lambda x: x) if len(list(g)) > 1]
input = ["andrew", "bob", "chris", "bob"]
input.sort()
output = [k for k, g in itertools.groupby(input, lambda x: x) if len(list(g)) > 1]
ruby
foo = ['andrew', 'bob', 'chris', 'bob']
foo.inject({}) {|h,v| h[v]=h[v].to_i+1; h}.reject{|k,v| v==1}.keys
foo.inject({}) {|h,v| h[v]=h[v].to_i+1; h}.reject{|k,v| v==1}.keys
scala
List("andrew", "bob", "chris", "bob")
.groupBy(identity)
.filter( person => person._2.size > 1)
.map(_._1)
.groupBy(identity)
.filter( person => person._2.size > 1)
.map(_._1)
val l = List("andrew", "bob", "chris", "bob")
l.diff(l.distinct)
l.diff(l.distinct)
Fetch an element of a list by index
Given the list
[One, Two, Three, Four, Five], fetch the third element ('Three')
clojure
(nth '[One Two Three Four Five] 2)
cpp
String^ result = list[2];
csharp
string[] items = new string[] { "One", "Two", "Three", "Four", "Five" };
List<string> list = new List<string>(items);
string third = list[2]; // "Three"
List<string> list = new List<string>(items);
string third = list[2]; // "Three"
// Make sure you import the System.Linq namespace.
// This is not the preferred way of indexing if you are using Lists.
string[] items = new string[] { "One", "Two", "Three", "Four", "Five" };
IEnumerable<string> list = new List<string>(items);
string third = list.ElementAt(2); // Three
// This is not the preferred way of indexing if you are using Lists.
string[] items = new string[] { "One", "Two", "Three", "Four", "Five" };
IEnumerable<string> list = new List<string>(items);
string third = list.ElementAt(2); // Three
erlang
Result = lists:nth(3, List),
Result = element(3, list_to_tuple(List)),
{Left, _} = lists:split(3, List), Result = lists:last(Left),
Result = nth0(2, List),
fantom
["One", "Two", "Three", "Four", "Five"][2]
["One", "Two", "Three", "Four", "Five"].get(2)
fsharp
let result = List.nth ["One"; "Two"; "Three"; "Four"; "Five"] 2
groovy
list = ['One', 'Two', 'Three', 'Four', 'Five']
result = list[2] // index starts at 0
result = list[2] // index starts at 0
haskell
let a = [1..5]
let b = a !! 2
print b
let b = a !! 2
print b
java
String result = list.get(2);
ocaml
let third = List.nth [ "One"; "Two"; "Three"; "Four"; "Five" ] 3;;
perl
qw(One Two Three Four Five)[2];
@list = qw(One Two Three Four Five);
$list[2];
$list[2];
python
list = ['One', 'Two', 'Three', 'Four', 'Five']
list[2]
list[2]
ruby
list = ['One', 'Two', 'Three', 'Four', 'Five']
list[2]
list[2]
['One', 'Two', 'Three', 'Four', 'Five'].fetch(2)
list = ['One', 'Two', 'Three', 'Four', 'Five']
list.at(2)
list.at(2)
['One', 'Two', 'Three', 'Four', 'Five'][2] # <= note the [2] at end of array
scala
val result = list(2)
Fetch the last element of a list
Given the list
[Red, Green, Blue], access the last element ('Blue')
clojure
(last '[One Two Three Four Five])
cpp
String^ result = list[list->Count - 1];
string last_elem = lst.back();
csharp
string[] items = new string[] { "Red", "Green", "Blue" };
List<string> list = new List<string>(items);
string last = list[list.Count - 1]; // "Blue"
List<string> list = new List<string>(items);
string last = list[list.Count - 1]; // "Blue"
// Make sure you import the System.Linq namespace.
// This is not the preferred way of finding the last element if you are using Lists.
string[] items = new string[] { "Red", "Green", "Blue" };
IEnumerable<string> list = new List<string>(items);
string last = list.Last(); // "Blue"
// This is not the preferred way of finding the last element if you are using Lists.
string[] items = new string[] { "Red", "Green", "Blue" };
IEnumerable<string> list = new List<string>(items);
string last = list.Last(); // "Blue"
erlang
Result = lists:last(List),
Result = last(List),
Result = hd(lists:reverse(List)),
Result = lists:nth(length(List), List),
fantom
["Red", "Green", "Blue"][-1]
["One", "Two", "Three", "Four", "Five"].last
fsharp
let last list =
let rec last' list' =
match list' with
| [x] -> x
| x :: xs -> last' xs
if List.is_empty list then failwith "empty list" else last' list
// ------
let result = last list
let rec last' list' =
match list' with
| [x] -> x
| x :: xs -> last' xs
if List.is_empty list then failwith "empty list" else last' list
// ------
let result = last list
let result = (List.nth list ((List.length list) - 1))
let result = (List.hd (List.rev list))
groovy
list = ['Red', 'Green', 'Blue']
result = list[-1]
result = list[-1]
haskell
last ["Red", "Green", "Blue"]
java
String result = list.get(list.size() - 1);
ocaml
let list = [ "Red"; "Green"; "Blue" ] in
let last = List.nth list ( (List.length list) - 1 );;
let last = List.nth list ( (List.length list) - 1 );;
let list = [ "Red"; "Green"; "Blue" ] in
let last = List.hd (List.rev list);;
let last = List.hd (List.rev list);;
let list_last l =
let rec aux h q =
match q with
| [] -> h
| h :: q -> aux h q in
match l with
| [] -> invalid_arg "list_last"
| h :: q -> aux h q
;;
list_last ["Red"; "Green"; "Blue"]
let rec aux h q =
match q with
| [] -> h
| h :: q -> aux h q in
match l with
| [] -> invalid_arg "list_last"
| h :: q -> aux h q
;;
list_last ["Red"; "Green"; "Blue"]
perl
qw(Red Green Blue)[-1];
@list = qw(Red Green Blue);
$list[-1];
$list[-1];
python
list = ['Red', 'Green', 'Blue']
list[-1]
list[-1]
ruby
['Red', 'Green', 'Blue'][-1]
['Red', 'Green', 'Blue'].at(-1)
['Red', 'Green', 'Blue'].last
['Red', 'Green', 'Blue'].fetch(-1)
scala
val result = list.last
val result = (list.drop(list.length - 1)).head
Find the common items in two lists
Given two lists, find the common items. E.g. given beans =
['broad', 'mung', 'black', 'red', 'white'] and colors = ['black', 'red', 'blue', 'green'], what are the bean varieties that are also color names?
clojure
(use 'clojure.set)
(let [beans '[broad mung black red white]
colors '[black red blue green]]
(intersection (set beans) (set colors)))
(let [beans '[broad mung black red white]
colors '[black red blue green]]
(intersection (set beans) (set colors)))
cpp
array<String^>^ inbeans = {"broad", "mung", "black", "red", "white"};
Generic::ICollection<String^>^ beans = makeSET<String^>(gcnew Generic::List<String^>((Generic::IEnumerable<String^>^) inbeans));
array<String^>^ incolors = {"black", "red", "blue", "green"};
Generic::ICollection<String^>^ colors = makeSET<String^>(gcnew Generic::List<String^>((Generic::IEnumerable<String^>^) incolors));
Generic::ICollection<String^>^ result = intersectSET<String^>(beans, colors);
Generic::ICollection<String^>^ beans = makeSET<String^>(gcnew Generic::List<String^>((Generic::IEnumerable<String^>^) inbeans));
array<String^>^ incolors = {"black", "red", "blue", "green"};
Generic::ICollection<String^>^ colors = makeSET<String^>(gcnew Generic::List<String^>((Generic::IEnumerable<String^>^) incolors));
Generic::ICollection<String^>^ result = intersectSET<String^>(beans, colors);
csharp
// Make sure you import the System.Linq namespace.
// This example uses arrays as the underlying implementation, but any IEnumerable type can be used - including List.
IEnumerable<string> beans = new string[] { "beans", "mung", "black", "red", "white" };
IEnumerable<string> colors = new string[] { "black", "red", "blue", "green" };
var intersect = beans.Intersect(colors); // ['red', 'black']
// This example uses arrays as the underlying implementation, but any IEnumerable type can be used - including List.
IEnumerable<string> beans = new string[] { "beans", "mung", "black", "red", "white" };
IEnumerable<string> colors = new string[] { "black", "red", "blue", "green" };
var intersect = beans.Intersect(colors); // ['red', 'black']
erlang
Beans = sets:from_list([broad, mung, black, red, white]), Colors = sets:from_list([black, red, blue, green]),
Common = sets:to_list(sets:intersection(Beans, Colors)),
Common = sets:to_list(sets:intersection(Beans, Colors)),
fantom
beans := ["broad", "mung", "black", "red", "white"]
colors := ["black", "red", "blue", "green"]
echo(beans.intersection(colors))
colors := ["black", "red", "blue", "green"]
echo(beans.intersection(colors))
fsharp
let beans = (Set.of_list ["broad"; "mung"; "black"; "red"; "white"])
let colors = (Set.of_list ["black"; "red"; "blue"; "green"])
let common = (Set.intersect beans colors)
let colors = (Set.of_list ["black"; "red"; "blue"; "green"])
let common = (Set.intersect beans colors)
let beans = Set ["broad"; "mung"; "black"; "red"; "white"]
let colors = Set ["black"; "red"; "blue"; "green"]
let common = Set.intersect beans colors
let colors = Set ["black"; "red"; "blue"; "green"]
let common = Set.intersect beans colors
// Iterates elements of
// list1 across Elements of list2 returning a list of string options
// as generated by List.tryFind
let findCommon(list1 : 'a list, list2 : 'a list) : 'a list =
list1 |> List.map(fun y -> list2 |> List.tryFind(fun x -> y = x))
// Iterates elements of string option list generated above
// returning a string list containing common elements of List1 and List2
|> List.fold(fun acc x -> if x <> None then x.Value::acc else acc) []
// reverse order of list (can't seem to make List.foldBack work for this
|> List.rev
let beans = ["broad"; "mung"; "black"; "red"; "white"]
let colors = ["black"; "red"; "blue"; "green"]
printfn "%A" (findCommon(beans, colors)) ;;
// list1 across Elements of list2 returning a list of string options
// as generated by List.tryFind
let findCommon(list1 : 'a list, list2 : 'a list) : 'a list =
list1 |> List.map(fun y -> list2 |> List.tryFind(fun x -> y = x))
// Iterates elements of string option list generated above
// returning a string list containing common elements of List1 and List2
|> List.fold(fun acc x -> if x <> None then x.Value::acc else acc) []
// reverse order of list (can't seem to make List.foldBack work for this
|> List.rev
let beans = ["broad"; "mung"; "black"; "red"; "white"]
let colors = ["black"; "red"; "blue"; "green"]
printfn "%A" (findCommon(beans, colors)) ;;
groovy
beans = ['broad', 'mung', 'black', 'red', 'white']
colors = ['black', 'red', 'blue', 'green']
common = beans.intersect(colors)
assert common == ['black', 'red']
colors = ['black', 'red', 'blue', 'green']
common = beans.intersect(colors)
assert common == ['black', 'red']
haskell
import Data.List
beans = ["broad", "mung", "black", "red", "white"]
colors = ["black", "red", "blue", "green"]
main = print (intersect beans colors)
beans = ["broad", "mung", "black", "red", "white"]
colors = ["black", "red", "blue", "green"]
main = print (intersect beans colors)
java
List beans = Arrays.asList(new String[]{"broad", "mung", "black", "red", "white"});
List colors = Arrays.asList(new String[]{"black", "red", "blue", "green"});
List common = ListUtils.intersection(beans, colors);
List colors = Arrays.asList(new String[]{"black", "red", "blue", "green"});
List common = ListUtils.intersection(beans, colors);
ocaml
let beans = ["broad"; "mung"; "black"; "red"; "white"]
let colors = ["black"; "red"; "blue"; "green"]
let f common c = if List.mem c beans then c::common else common
let common = List.fold_left f [] colors;;
(* common will contain a list with the common elements *)
let colors = ["black"; "red"; "blue"; "green"]
let f common c = if List.mem c beans then c::common else common
let common = List.fold_left f [] colors;;
(* common will contain a list with the common elements *)
(* using standard (functorized) sets *)
module SetTools(ASet: Set.S) =
struct
let of_list l =
List.fold_left (fun acc e -> ASet.add e acc) ASet.empty l
let find_common l1 l2 =
ASet.elements (ASet.inter (of_list l1) (of_list l2))
end
module StringSet = Set.Make(String)
module StringSetTools = SetTools(StringSet)
;;
let beans = ["broad"; "mung"; "black"; "red"; "white"] in
let colors = ["black"; "red"; "blue"; "green"] in
StringSetTools.find_common beans colors;;
module SetTools(ASet: Set.S) =
struct
let of_list l =
List.fold_left (fun acc e -> ASet.add e acc) ASet.empty l
let find_common l1 l2 =
ASet.elements (ASet.inter (of_list l1) (of_list l2))
end
module StringSet = Set.Make(String)
module StringSetTools = SetTools(StringSet)
;;
let beans = ["broad"; "mung"; "black"; "red"; "white"] in
let colors = ["black"; "red"; "blue"; "green"] in
StringSetTools.find_common beans colors;;
perl
@beans = qw(broad mung black red white);
@colors = qw(black red blue green);
@seen{@beans} = ();
for (@colors) {
push(@intersection, $_) if exists($seen{$_});
}
print join(', ', @intersection);
@colors = qw(black red blue green);
@seen{@beans} = ();
for (@colors) {
push(@intersection, $_) if exists($seen{$_});
}
print join(', ', @intersection);
@beans = qw(broad mung black red white);
@colors = qw(black red blue green);
my %colors_hash = map { $_ => 1 } @colors;
my @intersection = grep { $colors_hash{$_} } @beans;
print join(', ', @intersection),"\n";
@colors = qw(black red blue green);
my %colors_hash = map { $_ => 1 } @colors;
my @intersection = grep { $colors_hash{$_} } @beans;
print join(', ', @intersection),"\n";
@beans = qw/broad mung black red white/;
@colors = qw/black red blue green/;
print join ', ', grep { $_ ~~ @colors } @beans;
@colors = qw/black red blue green/;
print join ', ', grep { $_ ~~ @colors } @beans;
python
beans = ['broad', 'mung', 'black', 'red', 'white']
colors = ['black', 'red', 'blue', 'green']
common = [b for b in beans if b in colors]
colors = ['black', 'red', 'blue', 'green']
common = [b for b in beans if b in colors]
beans = ['broad', 'mung', 'black', 'red', 'white']
colors = ['black', 'red', 'blue', 'green']
common = set(beans) & set(colors)
colors = ['black', 'red', 'blue', 'green']
common = set(beans) & set(colors)
ruby
common = (beans.intersection(colors)).to_a
scala
val beans = "broad" :: "mung" :: "black" :: "red" :: "white" :: Nil
val colors = "black" :: "red" :: "blue" :: "green" :: Nil
val common = beans intersect colors
val colors = "black" :: "red" :: "blue" :: "green" :: Nil
val common = beans intersect colors
Display the unique items in a list
Display the unique items in a list, e.g. given ages =
[18, 16, 17, 18, 16, 19, 14, 17, 19, 18], display the unique elements, i.e. with duplicates removed.
clojure
;; returns a set
(set [18, 16, 17, 18, 16, 19, 14, 17, 19, 18])
;;#{14 16 17 18 19}
;; returns a lazy sequence of the unique elements
(distinct [18, 16, 17, 18, 16, 19, 14, 17, 19, 18])
;;(18 16 17 19 14)
(set [18, 16, 17, 18, 16, 19, 14, 17, 19, 18])
;;#{14 16 17 18 19}
;; returns a lazy sequence of the unique elements
(distinct [18, 16, 17, 18, 16, 19, 14, 17, 19, 18])
;;(18 16 17 19 14)
cpp
array<int>^ input = {18, 16, 17, 18, 16, 19, 14, 17, 19, 18};
Generic::List<int>^ ages = gcnew Generic::List<int>((Generic::IEnumerable<int>^) input);
Generic::ICollection<int>^ result = makeSET<int>(ages);
Generic::List<int>^ ages = gcnew Generic::List<int>((Generic::IEnumerable<int>^) input);
Generic::ICollection<int>^ result = makeSET<int>(ages);
list<int> input;
input += 18, 16, 17, 18, 16, 19, 14, 17, 19, 18;
input.sort();
unique_copy(input.begin(), input.end(), ostream_iterator<int>(cout, "\n"));
input += 18, 16, 17, 18, 16, 19, 14, 17, 19, 18;
input.sort();
unique_copy(input.begin(), input.end(), ostream_iterator<int>(cout, "\n"));
csharp
using System.Collections.Generic;
using System.Linq;
public class UniqueElements {
public static void Main() {
var list = new List<int>() { 18, 16, 17, 18, 16, 19, 14, 17, 19, 18 };
var uniques = list.Distinct();
}
}
using System.Linq;
public class UniqueElements {
public static void Main() {
var list = new List<int>() { 18, 16, 17, 18, 16, 19, 14, 17, 19, 18 };
var uniques = list.Distinct();
}
}
erlang
Ages = sets:to_list(sets:from_list([18, 16, 17, 18, 16, 19, 14, 17, 19, 18])), io:format("~w~n", [Ages]).
lists:usort([18, 16, 17, 18, 16, 19, 14, 17, 19, 18]).
fantom
uniqueAges := [18, 16, 17, 18, 16, 19, 14, 17, 19, 18].unique
echo(uniqueAges)
echo(uniqueAges)
fsharp
(Set.ofList [18; 16; 17; 18; 16; 19; 14; 17; 19; 18]) |> Set.iter (fun age -> printf "%d, " age)
groovy
ages = [18, 16, 17, 18, 16, 19, 14, 17, 19, 18]
println ages.unique()
println ages.unique()
ages = [18, 16, 17, 18, 16, 19, 14, 17, 19, 18]
unique = ages as Set
println unique
unique = ages as Set
println unique
haskell
import Data.List
ages = [18, 16, 17, 18, 16, 19, 14, 17, 19, 18]
uniqueAges = nub ages
ages = [18, 16, 17, 18, 16, 19, 14, 17, 19, 18]
uniqueAges = nub ages
java
Set<Integer> ages = new TreeSet<Integer>(Arrays.asList(new Integer[]{18, 16, 17, 18, 16, 19, 14, 17, 19, 18}));
System.out.println(ages);
System.out.println(ages);
ocaml
let ages = [18; 16; 17; 18; 16; 19; 14; 17; 19; 18]
let f res e = if List.mem e res then res else e::res
let unique = List.fold_left f [] ages;;
let f res e = if List.mem e res then res else e::res
let unique = List.fold_left f [] ages;;
(* using standard (functorized) sets *)
module SetTools(ASet: Set.S) =
struct
let of_list l =
List.fold_left (fun acc e -> ASet.add e acc) ASet.empty l
let unique l =
ASet.elements (of_list l)
end
module Integer =
struct
type t = int
let compare (x:t) y = Pervasives.compare x y
end
module IntegerSet = Set.Make(Integer)
module IntegerSetTools = SetTools(IntegerSet)
;;
IntegerSetTools.unique [18; 16; 17; 18; 16; 19; 14; 17; 19; 18];;
module SetTools(ASet: Set.S) =
struct
let of_list l =
List.fold_left (fun acc e -> ASet.add e acc) ASet.empty l
let unique l =
ASet.elements (of_list l)
end
module Integer =
struct
type t = int
let compare (x:t) y = Pervasives.compare x y
end
module IntegerSet = Set.Make(Integer)
module IntegerSetTools = SetTools(IntegerSet)
;;
IntegerSetTools.unique [18; 16; 17; 18; 16; 19; 14; 17; 19; 18];;
perl
@ages = (18, 16, 17, 18, 16, 19, 14, 17, 19, 18);
@seen{@ages} = ();
@unique = keys %seen;
print join(', ', @unique);
@seen{@ages} = ();
@unique = keys %seen;
print join(', ', @unique);
@ages = (18, 16, 17, 18, 16, 19, 14, 17, 19, 18);
@unique = grep(!$seen{$_}++, @ages);
print join(', ', @unique);
@unique = grep(!$seen{$_}++, @ages);
print join(', ', @unique);
@ages = (18, 16, 17, 18, 16, 19, 14, 17, 19, 18);
print join(', ', grep(!$seen{$_}++, @ages));
print join(', ', grep(!$seen{$_}++, @ages));
@ages = (18, 16, 17, 18, 16, 19, 14, 17, 19, 18);
for (@ages) {
push(@unique, $_) unless $seen{$_}++;
}
print join(', ', @unique);
for (@ages) {
push(@unique, $_) unless $seen{$_}++;
}
print join(', ', @unique);
use List::MoreUtils qw(uniq);
@ages = (18, 16, 17, 18, 16, 19, 14, 17, 19, 18);
print join(', ', uniq(@ages));
@ages = (18, 16, 17, 18, 16, 19, 14, 17, 19, 18);
print join(', ', uniq(@ages));
python
ages = [18, 16, 17, 18, 16, 19, 14, 17, 19, 18]
unique_ages = list(set(ages))
unique_ages = list(set(ages))
ruby
ages = [18, 16, 17, 18, 16, 19, 14, 17, 19, 18]
p ages.uniq
p ages.uniq
ages = [18, 16, 17, 18, 16, 19, 14, 17, 19, 18]
ages.uniq!
p ages
ages.uniq!
p ages
ages = (Set.new [18, 16, 17, 18, 16, 19, 14, 17, 19, 18]).to_a
p ages
p ages
scala
val ages = (18 :: 16 :: 17 :: 18 :: 16 :: 19 :: 14 :: 17 :: 19 :: 18 :: Nil) removeDuplicates
Remove an element from a list by index
Given the list
[Apple, Banana, Carrot], remove the first element to produce the list [Banana, Carrot]
clojure
(let [fruit ["Apple" "Banana" "Carrot"]
index 0]
(concat
(take index fruit)
(drop (+ index 1) fruit)))
index 0]
(concat
(take index fruit)
(drop (+ index 1) fruit)))
cpp
fruit->RemoveAt(0);
csharp
class Solution1516
{
static void Main()
{
List<string> fruit = new List<string>() { "Apple", "Banana", "Carrot" };
fruit.RemoveAt(0);
}
}
{
static void Main()
{
List<string> fruit = new List<string>() { "Apple", "Banana", "Carrot" };
fruit.RemoveAt(0);
}
}
erlang
Result = tl(List),
[_|Result] = List,
N = 1, {Left, Right} = lists:split(N - 1, List), Result = Left ++ tl(Right),
Result = drop(1, List),
fantom
list := ["Apple", "Banana", "Carrot"]
list.removeAt(0)
list.removeAt(0)
fsharp
let split_at list n =
let rec split_at' list' n' left right =
match list' with
| [] -> (List.rev left, List.rev right)
| x :: xs -> if n' <= n then split_at' xs (n' + 1) (x :: left) right else split_at' xs (n' + 1) left (x :: right)
split_at' list 0 [] []
// ------
let (_, right) = split_at fruit 0
let rec split_at' list' n' left right =
match list' with
| [] -> (List.rev left, List.rev right)
| x :: xs -> if n' <= n then split_at' xs (n' + 1) (x :: left) right else split_at' xs (n' + 1) left (x :: right)
split_at' list 0 [] []
// ------
let (_, right) = split_at fruit 0
let drop list n =
if n <= 0 then
list
else
let (_, right) = split_at list (n - 1)
right
// ------
let result = (drop fruit 1)
if n <= 0 then
list
else
let (_, right) = split_at list (n - 1)
right
// ------
let result = (drop fruit 1)
groovy
// to produce a new list
newlist = list.tail() // for 'Apple' at start
newlist = list - 'Apple' // for 'Apple' anywhere
newlist = list.tail() // for 'Apple' at start
newlist = list - 'Apple' // for 'Apple' anywhere
// mutate original list
list.remove(0)
list.remove(0)
haskell
deleteNth n xs | n > 0 = take (n-1) xs ++ drop n xs
main = print $ deleteNth 1 [1..3]
main = print $ deleteNth 1 [1..3]
fruit :: [String]
fruit = ["Apple", "Banana", "Carrot"]
main :: IO ()
main = putStrLn $ show $ tail fruit
fruit = ["Apple", "Banana", "Carrot"]
main :: IO ()
main = putStrLn $ show $ tail fruit
java
list.remove(0);
ocaml
let delete_at i al =
if i < 0 || i >= List.length al then
invalid_arg "delete_at"
else
let rec del i l =
match l with
| [] -> []
| h::t when i = 0 -> t
| h::t -> h :: del (i-1) t
in
del i al
;;
if i < 0 || i >= List.length al then
invalid_arg "delete_at"
else
let rec del i l =
match l with
| [] -> []
| h::t when i = 0 -> t
| h::t -> h :: del (i-1) t
in
del i al
;;
let rem_first l =
match l with
| [] -> []
| h::t -> t
;;
match l with
| [] -> []
| h::t -> t
;;
List.tl ["Apple"; "Banana"; "Carrot"]
perl
@list = qw(Apple Banana Carrot);
shift @list;
shift @list;
@list = qw(Apple Banana Carrot);
$offset = 0;
splice(@list, $offset, 1);
$offset = 0;
splice(@list, $offset, 1);
python
myList = ['Apple', 'Banana', 'Carrot']
print myList
del myList[0]
# or
myList.pop(0) # returns 'Apple'
print myList
print myList
del myList[0]
# or
myList.pop(0) # returns 'Apple'
print myList
ruby
['Apple', 'Banana', 'Carrot'].shift
fruit.delete_at(0)
scala
val (fl, fr) = fruit.splitAt(0) ; fruit = fl ::: fr.tail
fruit = fruit.tail
fruit = fruit.drop(1)
fruits = fruits.remove(fruits.indexOf(_) == 0)
Remove the last element of a list
clojure
(pop ["Apple" "Banana" "Carrot"])
cpp
fruit->RemoveAt(fruit->Count - 1);
csharp
List<string> fruits = new List() { "apple", "banana", "cherry" };
fruits.RemoveAt(fruits.Length - 1);
fruits.RemoveAt(fruits.Length - 1);
erlang
Result = init(List),
Result = take(length(List) - 1, List),
Result = lists:reverse(tl(lists:reverse(List))),
fantom
list := ["Apple", "Banana", "Carrot"]
list.removeAt(-1)
list.removeAt(-1)
list := ["Apple", "Banana", "Carrot"]ยจ
list.pop
list.pop
fsharp
let take list n =
if n <= 0 then
list
else
let (left, _) = split_at list (n - 1)
left
// ------
let result = (take fruit ((List.length fruit) - 1))
if n <= 0 then
list
else
let (left, _) = split_at list (n - 1)
left
// ------
let result = (take fruit ((List.length fruit) - 1))
let but_last list =
let rec but_last' list' acc =
match list' with
| [x] -> List.rev acc
| x :: xs -> but_last' xs (x :: acc)
if List.is_empty list then [] else but_last' list []
// ------
let result = (but_last fruit)
let rec but_last' list' acc =
match list' with
| [x] -> List.rev acc
| x :: xs -> but_last' xs (x :: acc)
if List.is_empty list then [] else but_last' list []
// ------
let result = (but_last fruit)
groovy
list = ['Apple', 'Banana', 'Carrot']
// to produce a new list
newlist = list[0,1]
// to modify original list
list.remove(2)
// to produce a new list
newlist = list[0,1]
// to modify original list
list.remove(2)
haskell
ages = [1,2,3,4]
init ages
init ages
java
list.remove(list.size() - 1);
ocaml
let remove_last list =
match (List.rev list) with
| h::t -> List.rev t
| [] -> []
match (List.rev list) with
| h::t -> List.rev t
| [] -> []
let remove_last lst =
List.rev (List.tl (List.rev lst))
List.rev (List.tl (List.rev lst))
let list_remove_last l =
let rec aux h q acc =
match q with
| [] -> List.rev acc
| h2 :: q -> aux h2 q (h :: acc) in
match l with
| [] -> invalid_arg "list_remove_last"
| h :: q -> aux h q []
let rec aux h q acc =
match q with
| [] -> List.rev acc
| h2 :: q -> aux h2 q (h :: acc) in
match l with
| [] -> invalid_arg "list_remove_last"
| h :: q -> aux h q []
perl
pop @list;
python
myList = ['Apple', 'Banana', 'Carrot']
myList.pop()
myList.pop()
ruby
list = ['Apple', 'Banana', 'Carrot']
list.delete_at(-1)
list.delete_at(-1)
list = ['Apple', 'Banana', 'Carrot']
list.pop
list.pop
scala
fruit = fruit.init
fruit = fruit.take(fruit.length - 1)
Rotate a list
Given a list
["apple", "orange", "grapes", "bananas"], rotate it by removing the first item and placing it on the end to yield ["orange", "grapes", "bananas", "apple"]
clojure
(let [fruit ["apple" "orange" "grapes" "bananas"]]
(concat (rest fruit) [(first fruit)])
(concat (rest fruit) [(first fruit)])
cpp
fruit->Add(fruit[0]); fruit->RemoveAt(0);
rotate(fruit.begin(), fruit.begin()+1, fruit.end());
csharp
var lst = new LinkedList<String>(new String[] {"apple", "orange", "grapes", "banana"});
lst.AddLast(lst.First());
lst.DeleteFirst();
lst.AddLast(lst.First());
lst.DeleteFirst();
erlang
N = 1, {Left, Right} = lists:split(N, List), Result = Right ++ Left,
N = 1, Result = rotate(N, List),
fantom
list := ["apple", "orange", "grapes", "bananas"]
list.add(list.removeAt(0))
list.add(list.removeAt(0))
fsharp
let rotate list n =
if n <= 0 then
list
else
let (left, right) = split_at list (n - 1)
right @ left
// ------
let result = (rotate fruit 1)
if n <= 0 then
list
else
let (left, right) = split_at list (n - 1)
right @ left
// ------
let result = (rotate fruit 1)
groovy
first = items.head()
items = items.tail() + first
items = items.tail() + first
items = items[1..-1] + items[0]
items = items + items.remove(0)
haskell
main = print $ rotate ["apple", "orange", "grapes", "bananas"]
rotate xs | length xs < 2 = xs
| otherwise = tail xs ++ [head xs]
rotate xs | length xs < 2 = xs
| otherwise = tail xs ++ [head xs]
java
list.add(list.remove(0));
Collections.rotate(list, -1);
ocaml
let rotate list =
match list with
| head::tail -> tail@[head]
| [] -> []
match list with
| head::tail -> tail@[head]
| [] -> []
perl
@list = qw(apple, orange, grapes, bananas);
push @list, shift @list;
push @list, shift @list;
@list = qw(apple orange grapes bananas);
@list = @list[1..$#list,0];
@list = @list[1..$#list,0];
python
l = ["apple", "orange", "grapes", "bananas"]
first, l = l[0], l[1:] + l[:1]
first, l = l[0], l[1:] + l[:1]
fruit = ['apple', 'orange', 'grapes', 'bananas']
fruit.append(fruit.pop(0))
fruit.append(fruit.pop(0))
ruby
items = ["apple", "orange", "grapes", "bananas"]
items << first = items.shift
# items is rotated
# first contains the first value in the list
items << first = items.shift
# items is rotated
# first contains the first value in the list
scala
items = items.tail ::: List(items.head)
items = (items.head :: ((items.tail).reverse)).reverse
Gather together corresponding elements from multiple lists
Given several lists, gather together the first element from every list, the second element from every list, and so on for all corresponding index values in the lists. E.g. for these three lists, first =
['Bruce', 'Tommy Lee', 'Bruce'], last = ['Willis', 'Jones', 'Lee'], years = [1955, 1946, 1940] the result should produce 3 actors. The middle actor should be Tommy Lee Jones.
clojure
(defn gatherer [listOfLists]
(if (empty? (first listOfLists))
() ; the base case for recursion
(cons
(map first listOfLists) ; get the first element of each of the lists
(gatherer (map rest listOfLists)) ; gather all the subsequent ones
)
)
)
(def firstnames '("Bruce" "Tommy Lee" "Bruce"))
(def lastnames '("Willis" "Jones" "Lee"))
(def years '(1955 1946 1940))
(println (gatherer [firstnames lastnames years]))
; -> ((Bruce Willis 1955) (Tommy Lee Jones 1946) (Bruce Lee 1940))
(if (empty? (first listOfLists))
() ; the base case for recursion
(cons
(map first listOfLists) ; get the first element of each of the lists
(gatherer (map rest listOfLists)) ; gather all the subsequent ones
)
)
)
(def firstnames '("Bruce" "Tommy Lee" "Bruce"))
(def lastnames '("Willis" "Jones" "Lee"))
(def years '(1955 1946 1940))
(println (gatherer [firstnames lastnames years]))
; -> ((Bruce Willis 1955) (Tommy Lee Jones 1946) (Bruce Lee 1940))
(def firstnames ["Bruce" "Tommy Lee" "Bruce"])
(def lastnames ["Willis" "Jones" "Lee"])
(def years [1955 1946 1940])
(println (map (fn [f l y] [f l y]) firstnames lastnames years))
(def lastnames ["Willis" "Jones" "Lee"])
(def years [1955 1946 1940])
(println (map (fn [f l y] [f l y]) firstnames lastnames years))
cpp
array<String^>^ first = {"Bruce", "Tommy Lee", "Bruce"}; array<String^>^ last = {"Willis", "Jones", "Lee"}; array<String^>^ years = {"1955", "1946", "1940"};
array<String^>^ result = zip<String^>(",", first, last, years);
array<String^>^ result = zip<String^>(",", first, last, years);
list<string> first = { "Bruce", "Tommy Lee", "Bruce" };
list<string> last = {"Willis", "Jones", "Lee"};
list<int> years = {1955, 1946, 1940};
list<tuple<string,string,int> > actors;
for (firstIt = first.begin(), lastIt = last.begin(), yearIt = years.begin();
firstIt != first.end() && lastIt != last.end() && yearIt != years.end();
++firstIt, ++lastIt, ++yearIt)
actors.push_back(make_tuple(*firstIt, *lastIt, *yearIt));
list<string> last = {"Willis", "Jones", "Lee"};
list<int> years = {1955, 1946, 1940};
list<tuple<string,string,int> > actors;
for (firstIt = first.begin(), lastIt = last.begin(), yearIt = years.begin();
firstIt != first.end() && lastIt != last.end() && yearIt != years.end();
++firstIt, ++lastIt, ++yearIt)
actors.push_back(make_tuple(*firstIt, *lastIt, *yearIt));
csharp
String[] first = { "Bruce", "Tommy Lee", "Bruce" };
String[] last = { "Willis", "Jones", "Lee" };
int[] years = { 1955, 1946, 1940 };
var actors = first.Zip(last, (f, l) => Tuple.Create(f, l)).Zip(years, (t, y) => Tuple.Create(t.Item1, t.Item2, y)).ToArray();
Debug.Assert(actors[1].Equals(Tuple.Create("Tommy Lee", "Jones", 1946)));
String[] last = { "Willis", "Jones", "Lee" };
int[] years = { 1955, 1946, 1940 };
var actors = first.Zip(last, (f, l) => Tuple.Create(f, l)).Zip(years, (t, y) => Tuple.Create(t.Item1, t.Item2, y)).ToArray();
Debug.Assert(actors[1].Equals(Tuple.Create("Tommy Lee", "Jones", 1946)));
erlang
First = ['Bruce', 'Tommy Lee', 'Bruce'], Last = ['Willis', 'Jones', 'Lee'], Years = [1955, 1946, 1940],
Result = lists:zip3(First, Last, Years),
Result = lists:zip3(First, Last, Years),
fantom
r := [,]
first.size.times |Int i| { r.add([first[i], last[i], years[i]]) }
echo(r)
first.size.times |Int i| { r.add([first[i], last[i], years[i]]) }
echo(r)
fsharp
let result = (List.zip3 first last years)
groovy
first = ['Bruce', 'Tommy Lee', 'Bruce']
last = ['Willis', 'Jones', 'Lee']
years = [1955, 1946, 1940]
actors = [first, last, years].transpose()
assert actors.size() == 3
assert actors[1] == ['Tommy Lee', 'Jones', 1946]
last = ['Willis', 'Jones', 'Lee']
years = [1955, 1946, 1940]
actors = [first, last, years].transpose()
assert actors.size() == 3
assert actors[1] == ['Tommy Lee', 'Jones', 1946]
haskell
import Prelude hiding (last)
first = ["Bruce", "Tommy Lee", "Bruce"]
last = ["Willis", "Jones", "Lee"]
years = [1955, 1946, 1940]
actors = zip3 first last years
first = ["Bruce", "Tommy Lee", "Bruce"]
last = ["Willis", "Jones", "Lee"]
years = [1955, 1946, 1940]
actors = zip3 first last years
java
String[] first = new String[]{"Bruce", "Tommy Lee", "Bruce"};
String[] last = new String[]{"Willis", "Jones", "Lee"};
String[] years = new String[]{"1955", "1946", "1940"};
List<String[]> list = new ArrayList<String[]>(); list.add(first); list.add(last); list.add(years);
String[] result = zip(",", list);
String[] last = new String[]{"Willis", "Jones", "Lee"};
String[] years = new String[]{"1955", "1946", "1940"};
List<String[]> list = new ArrayList<String[]>(); list.add(first); list.add(last); list.add(years);
String[] result = zip(",", list);
ocaml
let rec combine3 f l y =
match f, l, y with
| [], [], [] -> []
| fh :: fq, lh :: lq, yh :: yq ->
(fh, lh, yh) :: combine3 fq lq yq
| _ -> invalid_arg "combine3"
;;
let first = ["Bruce"; "Tommy Lee"; "Bruce"] in
let last = ["Willis"; "Jones"; "Lee"] in
let years = [1955; 1946; 1940] in
combine3 first last years
match f, l, y with
| [], [], [] -> []
| fh :: fq, lh :: lq, yh :: yq ->
(fh, lh, yh) :: combine3 fq lq yq
| _ -> invalid_arg "combine3"
;;
let first = ["Bruce"; "Tommy Lee"; "Bruce"] in
let last = ["Willis"; "Jones"; "Lee"] in
let years = [1955; 1946; 1940] in
combine3 first last years
perl
my @first = ('Bruce', 'Tommy Lee', 'Bruce');
my @last = ('Willis', 'Jones', 'Lee');
my @years = (1955, 1946, 1940);
my @actors;
my $max = scalar @first;
for my $index (0 .. $max) {
push @actors, [ $first[$index], $last[$index], $years[$index] ];
};
my @last = ('Willis', 'Jones', 'Lee');
my @years = (1955, 1946, 1940);
my @actors;
my $max = scalar @first;
for my $index (0 .. $max) {
push @actors, [ $first[$index], $last[$index], $years[$index] ];
};
python
first = ['Bruce', 'Tommy Lee', 'Bruce']
last = ['Willis', 'Jones', 'Lee']
years = [1955, 1946, 1940]
actors = zip(first, last, years)
assert len(actors) == 3
assert actors[1] == ('Tommy Lee', 'Jones', 1946)
last = ['Willis', 'Jones', 'Lee']
years = [1955, 1946, 1940]
actors = zip(first, last, years)
assert len(actors) == 3
assert actors[1] == ('Tommy Lee', 'Jones', 1946)
ruby
first = ['Bruce', 'Tommy Lee', 'Bruce']; last = ['Willis', 'Jones', 'Lee']; years = [1955, 1946, 1940]
result = first.zip(last, years)
result = first.zip(last, years)
first = ['Bruce', 'Tommy Lee', 'Bruce']; last = ['Willis', 'Jones', 'Lee']; years = [1955, 1946, 1940]
result = [first, last, years].transpose
result = [first, last, years].transpose
scala
def zip3(l1 : List[_], l2 : List[_],l3 : List[_]) : List[Tuple3[_, _, _]] =
{
def zip3$ (l1$ : List[_], l2$ : List[_], l3$ : List[_], acc : List[Tuple3[_, _, _]]) : List[Tuple3[_, _, _]] = l1$ match
{
case Nil => acc reverse
case l1$head :: l1$tail => zip3$(l1$tail, l2$.tail, l3$.tail, Tuple3(l1$head, l2$.head, l3$.head) :: acc)
}
zip3$(l1, l2, l3, List[Tuple3[_,_,_]]())
}
// ------
val result = zip3(first, last, years)
{
def zip3$ (l1$ : List[_], l2$ : List[_], l3$ : List[_], acc : List[Tuple3[_, _, _]]) : List[Tuple3[_, _, _]] = l1$ match
{
case Nil => acc reverse
case l1$head :: l1$tail => zip3$(l1$tail, l2$.tail, l3$.tail, Tuple3(l1$head, l2$.head, l3$.head) :: acc)
}
zip3$(l1, l2, l3, List[Tuple3[_,_,_]]())
}
// ------
val result = zip3(first, last, years)
val first = List("Bruce", "Tommy Lee", "Bruce")
val last = List("Willis", "Jones", "Lee")
val years = List(1955, 1946, 1940)
val results = (first, last, years).zipped.toList
println(results)
val last = List("Willis", "Jones", "Lee")
val years = List(1955, 1946, 1940)
val results = (first, last, years).zipped.toList
println(results)
List Combinations
Given two source lists (or sets), generate a list (or set) of all the pairs derived by combining elements from the individual lists (sets). E.g. given suites =
['H', 'D', 'C', 'S'] and faces = ['2', '3', '4', '5', '6', '7', '8', '9', '10', 'J', 'Q', 'K', 'A'], generate the deck of 52 cards, confirm the deck size and check it contains an expected card, say 'Ace of Hearts'.
clojure
(def suites ["H" "D" "C" "S"])
(def faces [2 3 4 5 6 7 8 9 10 "J" "Q" "K" "A"])
(defn listCards [] (for [s suites f faces] [f s]))
(some (partial = ["A" "H"]) (listCards))
; -> true
(count (listCards))
; -> 52
(def faces [2 3 4 5 6 7 8 9 10 "J" "Q" "K" "A"])
(defn listCards [] (for [s suites f faces] [f s]))
(some (partial = ["A" "H"]) (listCards))
; -> true
(count (listCards))
; -> 52
cpp
Specialized::StringCollection^ cards = gcnew Specialized::StringCollection;
for each(String^ suite in suites)
for each(String^ face in faces)
cards->Add(makeCard(suite, face));
Console::WriteLine("Deck has {0} cards", cards.Count);
if (cards->Contains(makeCard("h", "A"))) Console::WriteLine("Deck contains 'Ace of hearts'"); else Console::WriteLine("'Ace of hearts' not in deck");
for each(String^ suite in suites)
for each(String^ face in faces)
cards->Add(makeCard(suite, face));
Console::WriteLine("Deck has {0} cards", cards.Count);
if (cards->Contains(makeCard("h", "A"))) Console::WriteLine("Deck contains 'Ace of hearts'"); else Console::WriteLine("'Ace of hearts' not in deck");
auto suites = {"h", "d", "c", "s"};
auto faces = {"2", "3", "4", "5", "6", "7", "8", "9", "10", "J", "Q", "K", "A"};
list<card> cards;
for (auto s: suites)
for (auto f: faces)
cards.push_back(make_pair(s,f));
cout << "Deck has " << cards.size() << " cards." << endl;
card ace_of_harts = make_pair("h", "A");
if (end(cards) != find_if(begin(cards), end(cards),
[&](const card& c) { return c == ace_of_harts; }))
cout << "Deck contain 'Ace of Harts'" << endl;
else
cout << "Deck lacks 'Ace of Harts'" << endl;
auto faces = {"2", "3", "4", "5", "6", "7", "8", "9", "10", "J", "Q", "K", "A"};
list<card> cards;
for (auto s: suites)
for (auto f: faces)
cards.push_back(make_pair(s,f));
cout << "Deck has " << cards.size() << " cards." << endl;
card ace_of_harts = make_pair("h", "A");
if (end(cards) != find_if(begin(cards), end(cards),
[&](const card& c) { return c == ace_of_harts; }))
cout << "Deck contain 'Ace of Harts'" << endl;
else
cout << "Deck lacks 'Ace of Harts'" << endl;
csharp
using System;
using System.Collections.Generic;
using System.Linq;
namespace Combinations
{
class Program
{
public static void Main(string[] args)
{
// Define the given lists
// Since List`1 implements the interface IEnumerable`1, this can easily be redefined as List`1.
IEnumerable<string> suites = new string[] { "H", "D", "C", "S" };
IEnumerable<string> faces = new string[] { "2", "3", "4", "5", "6", "7", "8", "9", "10", "J", "Q", "K", "A" };
// LINQ Query to perform a Cartesian product and create an anonymous type to hold the results.
// "var" is required to define this as an IEnumerable`1
var deck =
from suite in suites // For each suite in suites
from face in faces // Match it with a face in face.
select new
{
Suite = suite,
Face = face
};
// Verify the count (uses LINQ extension)
if (deck.Count() == 52)
{
Console.WriteLine("Count matches!");
}
// Verify that the Ace of Hearts is in the deck (uses LINQ extension)
if (deck.Contains(new {Suite = "H", Face = "A"}))
{
Console.WriteLine("Ace of Hearts found!");
}
// Example of how to iterate through the list.
// "var" here is required since we are using an anonymous type
foreach(var card in deck)
{
Console.WriteLine("Suite: {0} Face: {1}", card.Suite, card.Face);
}
// If you desire to work with a List`1, you can convert this to a normal list at any time:
Console.WriteLine("\nConverting to list!");
var list = deck.ToList();
Console.WriteLine("Suite: {0} Face: {1}", list[5].Suite, list[5].Face);
Console.WriteLine("List count: {0}", list.Count); // 52
Console.ReadLine();
}
}
}
using System.Collections.Generic;
using System.Linq;
namespace Combinations
{
class Program
{
public static void Main(string[] args)
{
// Define the given lists
// Since List`1 implements the interface IEnumerable`1, this can easily be redefined as List`1.
IEnumerable<string> suites = new string[] { "H", "D", "C", "S" };
IEnumerable<string> faces = new string[] { "2", "3", "4", "5", "6", "7", "8", "9", "10", "J", "Q", "K", "A" };
// LINQ Query to perform a Cartesian product and create an anonymous type to hold the results.
// "var" is required to define this as an IEnumerable`1
var deck =
from suite in suites // For each suite in suites
from face in faces // Match it with a face in face.
select new
{
Suite = suite,
Face = face
};
// Verify the count (uses LINQ extension)
if (deck.Count() == 52)
{
Console.WriteLine("Count matches!");
}
// Verify that the Ace of Hearts is in the deck (uses LINQ extension)
if (deck.Contains(new {Suite = "H", Face = "A"}))
{
Console.WriteLine("Ace of Hearts found!");
}
// Example of how to iterate through the list.
// "var" here is required since we are using an anonymous type
foreach(var card in deck)
{
Console.WriteLine("Suite: {0} Face: {1}", card.Suite, card.Face);
}
// If you desire to work with a List`1, you can convert this to a normal list at any time:
Console.WriteLine("\nConverting to list!");
var list = deck.ToList();
Console.WriteLine("Suite: {0} Face: {1}", list[5].Suite, list[5].Face);
Console.WriteLine("List count: {0}", list.Count); // 52
Console.ReadLine();
}
}
}
erlang
Cards = lists:foldl(fun (Suite, Acc) -> Acc ++ lists:flatmap(fun (Face) -> [{Suite, Face}] end, Faces) end, [], Suites),
io:format("Deck has ~B cards~n", [length(Cards)]),
IsMember = lists:member({h, 'A'}, Cards),
io:format("~s~n", [if IsMember -> "Deck contains 'Ace of Hearts'" ; true -> "'Ace of Hearts' not in deck" end]),
io:format("Deck has ~B cards~n", [length(Cards)]),
IsMember = lists:member({h, 'A'}, Cards),
io:format("~s~n", [if IsMember -> "Deck contains 'Ace of Hearts'" ; true -> "'Ace of Hearts' not in deck" end]),
Cards = sofs:to_external(sofs:product(sofs:set(Suites), sofs:set(Faces))),
io:format("Deck has ~B cards~n", [length(Cards)]),
IsMember = lists:member({h, 'A'}, Cards),
io:format("~s~n", [if IsMember -> "Deck contains 'Ace of Hearts'" ; true -> "'Ace of Hearts' not in deck" end]),
io:format("Deck has ~B cards~n", [length(Cards)]),
IsMember = lists:member({h, 'A'}, Cards),
io:format("~s~n", [if IsMember -> "Deck contains 'Ace of Hearts'" ; true -> "'Ace of Hearts' not in deck" end]),
Deck2 = [{S, V} || S <- [d, c, h, s], V <- [2, 3, 4, 5, 6, 7, 8, 9, 10, 'J', 'Q', 'K', 'A']],
52 = length(Deck2),
true = lists:member({h, 'A'}, Deck2).
52 = length(Deck2),
true = lists:member({h, 'A'}, Deck2).
fantom
r := [,]
["2","3","4","5","6","7","8","9","10","J","Q","K","A"].each |Str c|
{ ["H","D","C","S"].each |Str s| { r.add([c,s]) } }
q := ["A","H"]
result := r.contains(q)
echo("Deck size=${r.size}, contains $q? -> $result")
["2","3","4","5","6","7","8","9","10","J","Q","K","A"].each |Str c|
{ ["H","D","C","S"].each |Str s| { r.add([c,s]) } }
q := ["A","H"]
result := r.contains(q)
echo("Deck size=${r.size}, contains $q? -> $result")
fsharp
let cards = (List.fold_left (fun acc suite -> acc @ (List.map (fun face -> (suite, face)) faces)) [] suites)
printfn "Deck has %d cards" (List.length cards)
printfn "%s" (if (List.exists (fun e -> e = ("h", "A")) cards) then "Deck contains 'Ace of Hearts'" ; else "'Ace of Hearts' not in deck")
printfn "Deck has %d cards" (List.length cards)
printfn "%s" (if (List.exists (fun e -> e = ("h", "A")) cards) then "Deck contains 'Ace of Hearts'" ; else "'Ace of Hearts' not in deck")
let product (set1 : List<'a>) (set2 : List<'a>) : List<'a * 'a> =
let p = new ResizeArray<'a * 'a>()
for e1 in set1 do for e2 in set2 do p.Add(e1, e2) done done
Array.to_list (p.ToArray())
// ------
let cards = product suites faces
printfn "Deck has %d cards" (List.length cards)
printfn "%s" (if (List.exists (fun e -> e = ("h", "A")) cards) then "Deck contains 'Ace of Hearts'" ; else "'Ace of Hearts' not in deck")
let p = new ResizeArray<'a * 'a>()
for e1 in set1 do for e2 in set2 do p.Add(e1, e2) done done
Array.to_list (p.ToArray())
// ------
let cards = product suites faces
printfn "Deck has %d cards" (List.length cards)
printfn "%s" (if (List.exists (fun e -> e = ("h", "A")) cards) then "Deck contains 'Ace of Hearts'" ; else "'Ace of Hearts' not in deck")
let deck =
suites
|> List.map (fun s -> faces |> List.map (fun f -> (s, f)))
|> List.concat
printfn "Deck has %d cards" (List.length deck)
match deck |> List.exists (fun e -> e = ("h", "A")) with
| true -> printfn "Deck contains 'Ace of Hearts'"
| _ -> printfn "'Ace of Hearts' not in deck"
suites
|> List.map (fun s -> faces |> List.map (fun f -> (s, f)))
|> List.concat
printfn "Deck has %d cards" (List.length deck)
match deck |> List.exists (fun e -> e = ("h", "A")) with
| true -> printfn "Deck contains 'Ace of Hearts'"
| _ -> printfn "'Ace of Hearts' not in deck"
groovy
faces = ['2', '3', '4', '5', '6', '7', '8', '9', '10', 'J', 'Q', 'K', 'A']
suites = ['H', 'D', 'C', 'S']
deck = [faces, suites].combinations()
assert deck.size() == 52
assert ['A', 'H'] in deck
suites = ['H', 'D', 'C', 'S']
deck = [faces, suites].combinations()
assert deck.size() == 52
assert ['A', 'H'] in deck
haskell
import Data.List
suites = ["H", "D", "C", "S"]
faces = ["2", "3", "4", "5", "6", "7", "8", "9", "10", "J", "Q", "K", "A"]
main = do
let cards = [(s,f) | s <- suites, f <- faces ]
print (length cards)
print $ hasCard ("H", "A") "Ace of Hearts" cards
where hasCard t name cards = (if elem t cards then "Contains "
else "Does not contain") ++ name
suites = ["H", "D", "C", "S"]
faces = ["2", "3", "4", "5", "6", "7", "8", "9", "10", "J", "Q", "K", "A"]
main = do
let cards = [(s,f) | s <- suites, f <- faces ]
print (length cards)
print $ hasCard ("H", "A") "Ace of Hearts" cards
where hasCard t name cards = (if elem t cards then "Contains "
else "Does not contain") ++ name
java
SortedSet<AbstractMap.SimpleImmutableEntry<String, String> > cards =
new TreeSet<AbstractMap.SimpleImmutableEntry<String, String> >(new CardComparator());
for (String suite : suites)
for (String face : faces)
cards.add(new AbstractMap.SimpleImmutableEntry<String, String>(suite, face));
Boolean containsEntry = cards.contains(new AbstractMap.SimpleImmutableEntry<String, String>("h", "A"));
if (containsEntry) System.out.println("Deck contains 'Ace of Hearts'");
else System.out.println("'Ace of Hearts' not in deck");
new TreeSet<AbstractMap.SimpleImmutableEntry<String, String> >(new CardComparator());
for (String suite : suites)
for (String face : faces)
cards.add(new AbstractMap.SimpleImmutableEntry<String, String>(suite, face));
Boolean containsEntry = cards.contains(new AbstractMap.SimpleImmutableEntry<String, String>("h", "A"));
if (containsEntry) System.out.println("Deck contains 'Ace of Hearts'");
else System.out.println("'Ace of Hearts' not in deck");
ocaml
let suites = ["H"; "D"; "C"; "S"]
let faces = ["2";"3";"4";"5";"6";"7";"8";"9";"10";"J";"Q";"K";"A"]
let desk =
List.fold_left (fun acc y ->
List.fold_left (fun acc2 x ->
(x, y)::acc2
) acc faces
) [] suites
let () =
assert (List.length desk = 52);
if List.mem ("A", "H") desk
then print_endline "Ace of Hearts found!"
else print_endline "Ace of Hearts not found :("
let faces = ["2";"3";"4";"5";"6";"7";"8";"9";"10";"J";"Q";"K";"A"]
let desk =
List.fold_left (fun acc y ->
List.fold_left (fun acc2 x ->
(x, y)::acc2
) acc faces
) [] suites
let () =
assert (List.length desk = 52);
if List.mem ("A", "H") desk
then print_endline "Ace of Hearts found!"
else print_endline "Ace of Hearts not found :("
perl
@suites = qw(H D C S);
@faces = qw(2 3 4 5 6 7 8 9 10 J Q K A);
@deck = map { $suite=$_; map $suite.$_, @faces; } @suites;
print 'checking deck size: ' . (@deck == 52 ? 'pass' : 'fail') . "\n";
print 'deck contains "Ace of Hearts": ' . (grep(/^HA$/, @deck) ? 'true' : 'false') . "\n";
@faces = qw(2 3 4 5 6 7 8 9 10 J Q K A);
@deck = map { $suite=$_; map $suite.$_, @faces; } @suites;
print 'checking deck size: ' . (@deck == 52 ? 'pass' : 'fail') . "\n";
print 'deck contains "Ace of Hearts": ' . (grep(/^HA$/, @deck) ? 'true' : 'false') . "\n";
python
suites = ('H', 'D', 'C', 'S')
faces = ('2', '3', '4', '5', '6', '7', '8', '9', '10', 'J', 'Q', 'K', 'A')
deck = [(face,suite) for suite in suites for face in faces]
assert len(deck) == 52
assert ('A', 'H') in deck
faces = ('2', '3', '4', '5', '6', '7', '8', '9', '10', 'J', 'Q', 'K', 'A')
deck = [(face,suite) for suite in suites for face in faces]
assert len(deck) == 52
assert ('A', 'H') in deck
ruby
suites.each {|s| faces.each {|f| cards << [s, f]}}
puts "Deck %s \'Ace of Hearts\'" % if cards.include?(['h', 'A']) then "contains" else "does not contain" end
puts "Deck %s \'Ace of Hearts\'" % if cards.include?(['h', 'A']) then "contains" else "does not contain" end
scala
def product(set1 : List[_], set2 : List[_]) : List[Pair[_, _]] =
{
val p = new mutable.ArrayBuffer[Pair[_, _]]()
for (e1 <- set1) for (e2 <- set2) p += Pair(e1, e2)
p.toList
}
// ------
val cards = product(suites, faces)
printf("Deck has %d cards\n", cards.length)
if (cards.contains(Pair("h", "A"))) println("Deck contains 'Ace of Hearts'")
else println("'Ace of Hearts' not in this deck")
{
val p = new mutable.ArrayBuffer[Pair[_, _]]()
for (e1 <- set1) for (e2 <- set2) p += Pair(e1, e2)
p.toList
}
// ------
val cards = product(suites, faces)
printf("Deck has %d cards\n", cards.length)
if (cards.contains(Pair("h", "A"))) println("Deck contains 'Ace of Hearts'")
else println("'Ace of Hearts' not in this deck")
Perform an operation on every item of a list
Perform an operation on every item of a list, e.g.
for the list
the list of sizes of the strings, e.g.
for the list
["ox", "cat", "deer", "whale"] calculate
the list of sizes of the strings, e.g.
[2, 3, 4, 5]
clojure
(map count ["ox" "cat" "deer" "whale"])
cpp
list<string> words;
words.push_back("ox");
words.push_back("cat");
words.push_back("deer");
words.push_back("whale");
for (list<string>::iterator it = words.begin(); it != words.end(); ++it)
cout << it->size() << ' ';
cout << endl;
words.push_back("ox");
words.push_back("cat");
words.push_back("deer");
words.push_back("whale");
for (list<string>::iterator it = words.begin(); it != words.end(); ++it)
cout << it->size() << ' ';
cout << endl;
auto words = { "ox", "cat", "deer", "whale" };
list<size_t> word_sizes;
transform(begin(words),
end(words),
back_inserter(word_sizes),
[](const string& s) { return s.size(); });
list<size_t> word_sizes;
transform(begin(words),
end(words),
back_inserter(word_sizes),
[](const string& s) { return s.size(); });
csharp
using System.Collections.Generic;
public class OperationOnEach {
public static void Main() {
var list = new List<string>() { "ox", "cat", "deer", "whale" };
list.ForEach( System.Console.WriteLine );
}
}
public class OperationOnEach {
public static void Main() {
var list = new List<string>() { "ox", "cat", "deer", "whale" };
list.ForEach( System.Console.WriteLine );
}
}
erlang
lists:map(fun (X) ->length(X) end, List).
fantom
["ox", "cat", "deer", "whale"].map { it.size }
fsharp
let lengths = List.map String.length ["ox"; "cat"; "deer"; "whale"]
groovy
animals = ["ox", "cat", "deer", "whale"]
assert animals*.size() == [2, 3, 4, 5]
assert animals*.size() == [2, 3, 4, 5]
haskell
map length ["ox", "cat", "deer", "whale"]
java
public class SolutionXX {
public static void main(String[] args) {
String[] list = {"ox", "cat", "deer", "whale"};
for (String str : list) {
System.out.println(str.length() + " ");
}
}
}
public static void main(String[] args) {
String[] list = {"ox", "cat", "deer", "whale"};
for (String str : list) {
System.out.println(str.length() + " ");
}
}
}
ocaml
List.map String.length ["ox"; "cat"; "deer"; "whale"];;
perl
my @list = qw{ox cat deer whale};
my @lengths = map {length($_)} @list;
print "@list\n";
print "@lengths\n";
my @lengths = map {length($_)} @list;
print "@list\n";
print "@lengths\n";
python
print map(lambda x: len(x), ["ox", "cat", "deer", "whale"])
print [len(x) for x in ['ox', 'cat', 'deer', 'whale']]
ruby
["ox", "cat", "deer", "whale"].map{|i| i.length}
scala
val sizes = List("ox", "cat", "deer", "whale") map {_ size}
assert(sizes == List(2, 3, 4, 5))
val sizes = List("ox", "cat", "deer", "whale") map {_ size}
assert(sizes == List(2, 3, 4, 5))
Split a list of things into numbers and non-numbers
Given a list that might contain e.g. a string, an integer, a float and a date,
split the list into numbers and non-numbers.
split the list into numbers and non-numbers.
clojure
(def jumble [3 "Bill" 5.7 '("A" "B" "C")]) ; int, string, float, list
(defn numberNonNumberSorter [jumbledList]
(if (empty? jumbledList)
(hash-map :numbers [], :nonnumbers []) ; recursion base case - return two empty lists
(let [head (first jumbledList)] ; let <head> be the first element in the list
(let [tailresult (numberNonNumberSorter (rest jumbledList))] ; tailresult applies recursively to the remainder
(if (number? head) ; is head a number?
(hash-map
:numbers (cons head (tailresult :numbers)) ; add <head> to the numbers
:nonnumbers (tailresult :nonnumbers)) ; leave nonnumbers the same
(hash-map
:numbers (tailresult :numbers) ; leave numbers the same
:nonnumbers (cons head (tailresult :nonnumbers))) ; add <head> to nonnumbers
)
)
)
)
)
(println (numberNonNumberSorter jumble))
; -> {:nonnumbers (Bill (A B C)), :numbers (3 5.7)}
(defn numberNonNumberSorter [jumbledList]
(if (empty? jumbledList)
(hash-map :numbers [], :nonnumbers []) ; recursion base case - return two empty lists
(let [head (first jumbledList)] ; let <head> be the first element in the list
(let [tailresult (numberNonNumberSorter (rest jumbledList))] ; tailresult applies recursively to the remainder
(if (number? head) ; is head a number?
(hash-map
:numbers (cons head (tailresult :numbers)) ; add <head> to the numbers
:nonnumbers (tailresult :nonnumbers)) ; leave nonnumbers the same
(hash-map
:numbers (tailresult :numbers) ; leave numbers the same
:nonnumbers (cons head (tailresult :nonnumbers))) ; add <head> to nonnumbers
)
)
)
)
)
(println (numberNonNumberSorter jumble))
; -> {:nonnumbers (Bill (A B C)), :numbers (3 5.7)}
(group-by number? ["hello" 42 3.14 (Date.)])
cpp
typedef variant<int,float,string,date> dynamic;
class is_number : public static_visitor<bool>
{
public:
bool operator()(int &) const {
return true;
}
bool operator()(float &) const {
return true;
}
bool operator()(string &) const {
return false;
}
bool operator()(date &) const {
return false;
}
};
int main()
{
list<dynamic> lst;
list<dynamic> numbers;
list<dynamic> non_numbers;
lst += "hello", 3.14f, 42, date(2011,Aug,23);
BOOST_FOREACH(dynamic v, lst)
if (apply_visitor(is_number(), v))
numbers += v;
else
non_numbers += v;
class is_number : public static_visitor<bool>
{
public:
bool operator()(int &) const {
return true;
}
bool operator()(float &) const {
return true;
}
bool operator()(string &) const {
return false;
}
bool operator()(date &) const {
return false;
}
};
int main()
{
list<dynamic> lst;
list<dynamic> numbers;
list<dynamic> non_numbers;
lst += "hello", 3.14f, 42, date(2011,Aug,23);
BOOST_FOREACH(dynamic v, lst)
if (apply_visitor(is_number(), v))
numbers += v;
else
non_numbers += v;
#include <iostream>
#include <list>
#include <boost/any.hpp>
#include <boost/date_time/gregorian/gregorian.hpp>
#include <boost/foreach.hpp>
using namespace boost;
using namespace boost::gregorian;
using namespace std;
int main()
{
list<any> lst;
list<any> numbers;
list<any> non_numbers;
lst.push_back(string("hello"));
lst.push_back(42);
lst.push_back(3.14f);
lst.push_back(date(day_clock::local_day()));
BOOST_FOREACH(const any &a, lst)
try
{
numbers.push_back(any_cast<int>(a));
}
catch (bad_any_cast &e)
{
try
{
numbers.push_back(any_cast<float>(a));
}
catch (bad_any_cast &e)
{
non_numbers.push_back(a);
}
}
// float and int are now in 'numbers' and the rest in 'non_numbers'
}
#include <list>
#include <boost/any.hpp>
#include <boost/date_time/gregorian/gregorian.hpp>
#include <boost/foreach.hpp>
using namespace boost;
using namespace boost::gregorian;
using namespace std;
int main()
{
list<any> lst;
list<any> numbers;
list<any> non_numbers;
lst.push_back(string("hello"));
lst.push_back(42);
lst.push_back(3.14f);
lst.push_back(date(day_clock::local_day()));
BOOST_FOREACH(const any &a, lst)
try
{
numbers.push_back(any_cast<int>(a));
}
catch (bad_any_cast &e)
{
try
{
numbers.push_back(any_cast<float>(a));
}
catch (bad_any_cast &e)
{
non_numbers.push_back(a);
}
}
// float and int are now in 'numbers' and the rest in 'non_numbers'
}
csharp
using System;
using System.Collections.Generic;
using System.Linq;
// AFAIK, there just isn't a good way to do this in C#
public class ListSplitter {
public static bool IsNumeric(object o) {
var d = new Decimal();
return decimal.TryParse(o.ToString(), out d);
}
public static void Main() {
var list = new List<object>() { "foo", DateTime.Now, 1, "bar", 2.4 };
// the Where method does the work...
var numbers = list.Where( el => IsNumeric(el) );
var nonNumbers = list.Where( el => ! IsNumeric(el) );
}
}
using System.Collections.Generic;
using System.Linq;
// AFAIK, there just isn't a good way to do this in C#
public class ListSplitter {
public static bool IsNumeric(object o) {
var d = new Decimal();
return decimal.TryParse(o.ToString(), out d);
}
public static void Main() {
var list = new List<object>() { "foo", DateTime.Now, 1, "bar", 2.4 };
// the Where method does the work...
var numbers = list.Where( el => IsNumeric(el) );
var nonNumbers = list.Where( el => ! IsNumeric(el) );
}
}
erlang
% Wrapped call to the auxiliary function
number_split(Xs) ->
number_split(Xs, [], []).
% The auxiliary function
number_split([], Num, NonNum) ->
{Num, NonNum};
number_split([X|Xs], Num, NonNum) ->
case is_number(X) of
true ->
number_split(Xs, [X|Num], NonNum);
false ->
number_split(Xs, Num, [X|NonNum])
end.
number_split(Xs) ->
number_split(Xs, [], []).
% The auxiliary function
number_split([], Num, NonNum) ->
{Num, NonNum};
number_split([X|Xs], Num, NonNum) ->
case is_number(X) of
true ->
number_split(Xs, [X|Num], NonNum);
false ->
number_split(Xs, Num, [X|NonNum])
end.
List = ["hello", 25, 3.14, calendar:local_time()],
{Numbers, NonNumbers} = lists:partition(fun(E) -> is_number(E) end, List)
{Numbers, NonNumbers} = lists:partition(fun(E) -> is_number(E) end, List)
fantom
things := ["hello", 25, 3.14, Time.now]
numbers := things.findType(Num#)
nonNumbers := things.exclude { numbers.contains(it) }
numbers := things.findType(Num#)
nonNumbers := things.exclude { numbers.contains(it) }
fsharp
let (things:obj list) = [ "hello"; 25; 3.14; System.DateTime.Now ]
let isNumber (x:obj) =
match x with
| :? int | :? float | :? byte | :? decimal | :? int16 | :? int64 -> true
| _ -> false
let numbers, nonNumbers = things |> List.partition isNumber
let isNumber (x:obj) =
match x with
| :? int | :? float | :? byte | :? decimal | :? int16 | :? int64 -> true
| _ -> false
let numbers, nonNumbers = things |> List.partition isNumber
groovy
now = new Date()
things = ["hello", 25, 3.14, now]
(numbers, others) = things.split{ it instanceof Number }
assert numbers == [25, 3.14]
assert others == ["hello", now]
things = ["hello", 25, 3.14, now]
(numbers, others) = things.split{ it instanceof Number }
assert numbers == [25, 3.14]
assert others == ["hello", now]
haskell
import Data.List (partition)
type Date = String
data Things = TS String | TI Int | TD Date
deriving Show
main = do
let myList = [TI 1, TI 23, TS "Joe", TD "23/04/2009"]
print $ partition isNumber myList
where isNumber (TS _) = False
isNumber (TI _) = True
isNumber (TD _) = False
type Date = String
data Things = TS String | TI Int | TD Date
deriving Show
main = do
let myList = [TI 1, TI 23, TS "Joe", TD "23/04/2009"]
print $ partition isNumber myList
where isNumber (TS _) = False
isNumber (TI _) = True
isNumber (TD _) = False
java
public class NumbersSolution {
public static void main(String[] args) {
List<Object> items = Arrays.asList(new Object[] { new Date(), 12L, 15.4, 99, "x" } ) ;
List<Object> numbers = new ArrayList<Object>() ;
List<Object> nonNumbers = new ArrayList<Object>() ;
for (Object item : items )
(item instanceof Number ? numbers : nonNumbers).add(item) ;
}
}
public static void main(String[] args) {
List<Object> items = Arrays.asList(new Object[] { new Date(), 12L, 15.4, 99, "x" } ) ;
List<Object> numbers = new ArrayList<Object>() ;
List<Object> nonNumbers = new ArrayList<Object>() ;
for (Object item : items )
(item instanceof Number ? numbers : nonNumbers).add(item) ;
}
}
public class NumbersSolution {
public static void main() {
List<Object> numbers = new ArrayList<Object>() ;
List<Object> nonNumbers = new ArrayList<Object>() ;
for (Object item : new Object[] { new Date(), 12L, 15.4, 99, "x" } )
(item instanceof Number ? numbers : nonNumbers).add(item) ;
}
}
public static void main() {
List<Object> numbers = new ArrayList<Object>() ;
List<Object> nonNumbers = new ArrayList<Object>() ;
for (Object item : new Object[] { new Date(), 12L, 15.4, 99, "x" } )
(item instanceof Number ? numbers : nonNumbers).add(item) ;
}
}
ocaml
(* OCaml is a strongly statically typed language so it is not possible to mix
items of different types in a single list.
So here we use a list of strings, some of these strings represent a number *)
let is_a_number v =
try ignore(float_of_string v); true
with _ -> false
let numbers, others =
List.partition is_a_number ["Joe"; "3.14"; "8"; "hello"; "23/04/2009"]
(* ========================================================================== *)
(* If we really want to mix items of several types, we can declare a variant: *)
type item = Int of int | Float of float | String of string | Char of char
let is_a_number = function
| Float _ | Int _ -> true
| String _ | Char _ -> false
let numbers, others =
List.partition is_a_number [String "Joe"; Float 3.14; Int 8; Char 'Z']
items of different types in a single list.
So here we use a list of strings, some of these strings represent a number *)
let is_a_number v =
try ignore(float_of_string v); true
with _ -> false
let numbers, others =
List.partition is_a_number ["Joe"; "3.14"; "8"; "hello"; "23/04/2009"]
(* ========================================================================== *)
(* If we really want to mix items of several types, we can declare a variant: *)
type item = Int of int | Float of float | String of string | Char of char
let is_a_number = function
| Float _ | Int _ -> true
| String _ | Char _ -> false
let numbers, others =
List.partition is_a_number [String "Joe"; Float 3.14; Int 8; Char 'Z']
perl
use Scalar::Util qw(looks_like_number);
my @things = ('hello',25,3.14,scalar(localtime(time)));
my @numbers;
my @others;
for ( @things ) {
if ( looks_like_number $_ ) {
push @numbers, $_;
} else {
push @other, $_;
}
}
my @things = ('hello',25,3.14,scalar(localtime(time)));
my @numbers;
my @others;
for ( @things ) {
if ( looks_like_number $_ ) {
push @numbers, $_;
} else {
push @other, $_;
}
}
python
import re
data = '34234aff340980adf0e0fa0fefl' ## or ''.join(array)
nonDigits = re.findall(re.compile('\D'), data)
digits = re.findall(re.compile('\d'), data)
data = '34234aff340980adf0e0fa0fefl' ## or ''.join(array)
nonDigits = re.findall(re.compile('\D'), data)
digits = re.findall(re.compile('\d'), data)
ruby
now=Time.now
things=["hello", 25, 3.14, now]
numbers=things.select{|i| i.is_a? Numeric}
others=things-numbers
things=["hello", 25, 3.14, now]
numbers=things.select{|i| i.is_a? Numeric}
others=things-numbers
now=Time.now
things=["hello", 25, 3.14, now]
numbers, others=things.partition{|i| i.is_a? Numeric}
things=["hello", 25, 3.14, now]
numbers, others=things.partition{|i| i.is_a? Numeric}
scala
val now = new java.util.Date()
val result = List("hello", 25, 3.14, now) partition { _.isInstanceOf[Number] }
assert(result == (List(25, 3.14), List("hello", now)))
val result = List("hello", 25, 3.14, now) partition { _.isInstanceOf[Number] }
assert(result == (List(25, 3.14), List("hello", now)))
Test if a condition holds for all items of a list
Given a list, test if a certain logical condition (i.e. predicate) holds for all items of the list.
clojure
(every? #(> % 1) [2 3 4])
cpp
template <typename InputIterator, typename Predicate>
bool match_all(InputIterator first, InputIterator last, Predicate pred)
{
return find_if(first, last, !pred(_1)) == last;
}
bool match_all(InputIterator first, InputIterator last, Predicate pred)
{
return find_if(first, last, !pred(_1)) == last;
}
erlang
Result = lists:all(Pred, List).
fantom
echo([2,3,4].all{ it>1 })
fsharp
let rec IsAll predicate source =
let mutable acc = true
for e in source do
acc <- acc && (predicate e)
acc
let mutable acc = true
for e in source do
acc <- acc && (predicate e)
acc
groovy
[2,3,4].every{it > 1}
haskell
all (> 1) [2, 3, 4]
all (> 1) [2, 3, 4]
ocaml
(* from the interactive loop *)
# List.for_all (fun x -> x > 1) [2; 3; 4] ;;
- : bool = true
# List.for_all (fun x -> x > 1) [2; 3; 4] ;;
- : bool = true
python
all(x > 1 for x in [2,3,4])
ruby
[2, 3, 4].all? { |x| x > 1 }
scala
List(2, 3, 4).forall { _ > 1 }
List(2, 3, 4).forall { x => x > 1 }
Test if a condition holds for any items of a list
Given a list, test if a certain logical condition (i.e. predicate) holds for any items of the list.
clojure
; The standard library in Clojure has "not-any?" but (oddly enough) no "any?"
(defn any? [pred coll]
((complement not-any?) pred coll))
(any? #(> % 3) [2 3 4])
(defn any? [pred coll]
((complement not-any?) pred coll))
(any? #(> % 3) [2 3 4])
(some #(> % 3) [2 3 4])
cpp
template <typename InputIterator, typename Predicate>
bool match_any(InputIterator first, InputIterator last, Predicate pred)
{
return find_if(first, last, pred) != last;
}
bool match_any(InputIterator first, InputIterator last, Predicate pred)
{
return find_if(first, last, pred) != last;
}
erlang
Result = lists:any(Pred, List).
fantom
echo([2,3,4].any{ it==4 })
fsharp
let rec IsAny predicate source =
match source with
| [] -> false
| h::t ->
if (predicate h) then true
else (IsAny predicate t )
match source with
| [] -> false
| h::t ->
if (predicate h) then true
else (IsAny predicate t )
groovy
[2,3,4].any{it > 3}
haskell
any (> 1) [1, 2, 3]
ocaml
(* from the interactive loop: *)
# List.exists (fun x -> x > 3) [2; 3; 4] ;;
- : bool = true
# List.exists (fun x -> x > 3) [2; 3; 4] ;;
- : bool = true
python
any(x > 3 for x in [2, 3, 4])
ruby
[2, 3, 4].any? { |x| x > 3 }
scala
List(2, 3, 4).exists { _ > 3 }
List(2, 3, 4).exists { x => x > 3 }
