View Subcategory
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.
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)
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))
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),
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));
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'.
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
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
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).
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;
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]
python
print map(lambda x: len(x), ["ox", "cat", "deer", "whale"])
print [len(x) for x in ['ox', 'cat', 'deer', 'whale']]
clojure
(map count ["ox" "cat" "deer" "whale"])
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).
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(); });
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.
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)
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.)])
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)
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'
}
