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Define an empty list

Assign the variable "list" to a list with no elements
erlang
List = [],
cpp
Generic::List<String^>^ list = gcnew Generic::List<String^>();
std::list<std::string> list;

Define a static list

Define the list [One, Two, Three, Four, Five]
erlang
List = [one, two, three, four, five],
List = ['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^>();

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;

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";

Join the elements of a list, separated by commas

Given the list [Apple, Banana, Carrot] produce "Apple, Banana, Carrot"
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)]]).
cpp
String^ result = String::Join(L", ", fruit->ToArray());
string fruits[] = {"Apple", "Banana", "Carrot"};
string result = boost::algorithm::join(fruits, ", ");

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([Apple, Banana, Carrot]) = "Apple, Banana, and Carrot"
join([One, Two]) = "One and Two"
join([Lonely]) = "Lonely"
join([]) = ""
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).
%% 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)].

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);
}
}

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]]
erlang
Combinations =
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]].

cpp
Specialized::StringCollection^ combinations = gcnew Specialized::StringCollection;

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;

From a List Produce a List of Duplicate Entries

Taking a list:
["andrew", "bob", "chris", "bob"]

Write the code to produce a list of duplicates in the list:
["bob"]
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 = fun
([X | Xs], F) -> case lists:member(X, Xs) of
true -> [X | F(Xs, F)];
_ -> F(Xs, F)
end;
([], _) -> []
end,
Result = Fun(List, Fun).
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;
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;

Fetch an element of a list by index

Given the list [One, Two, Three, Four, Five], fetch the third element ('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),
cpp
String^ result = list[2];

Fetch the last element of a list

Given the list [Red, Green, Blue], access the last element ('Blue')
erlang
Result = lists:last(List),
Result = last(List),
Result = hd(lists:reverse(List)),
Result = lists:nth(length(List), List),
cpp
String^ result = list[list->Count - 1];
string last_elem = lst.back();

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?
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)),
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);

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.
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]).
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);
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"));

Remove an element from a list by index

Given the list [Apple, Banana, Carrot], remove the first element to produce the list [Banana, Carrot]
erlang
Result = tl(List),
[_|Result] = List,
N = 1, {Left, Right} = lists:split(N - 1, List), Result = Left ++ tl(Right),
Result = drop(1, List),
cpp
fruit->RemoveAt(0);

Remove the last element of a list

erlang
Result = init(List),
Result = take(length(List) - 1, List),
Result = lists:reverse(tl(lists:reverse(List))),
cpp
fruit->RemoveAt(fruit->Count - 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"]
erlang
N = 1, {Left, Right} = lists:split(N, List), Result = Right ++ Left,
N = 1, Result = rotate(N, List),
cpp
fruit->Add(fruit[0]); fruit->RemoveAt(0);
rotate(fruit.begin(), fruit.begin()+1, fruit.end());

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.
erlang
First = ['Bruce', 'Tommy Lee', 'Bruce'], Last = ['Willis', 'Jones', 'Lee'], Years = [1955, 1946, 1940],

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);
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 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'.
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]),
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]),
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).

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");
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;

Perform an operation on every item of a list

Perform an operation on every item of a list, e.g.
for the list ["ox", "cat", "deer", "whale"] calculate
the list of sizes of the strings, e.g. [2, 3, 4, 5]
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;
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(); });

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.
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.
List = ["hello", 25, 3.14, calendar:local_time()],
{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;
#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'
}

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.
erlang
Result = lists:all(Pred, List).
cpp
template <typename InputIterator, typename Predicate>
bool match_all(InputIterator first, InputIterator last, Predicate pred)
{
return find_if(first, last, !pred(_1)) == last;
}

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.
erlang
Result = lists:any(Pred, List).
cpp
template <typename InputIterator, typename Predicate>
bool match_any(InputIterator first, InputIterator last, Predicate pred)
{
return find_if(first, last, pred) != last;
}