-spec all(Pred, List) -> boolean() when Pred :: fun((Elem :: T) -> boolean()), List :: [T], T :: term().

Returns true if Pred(Elem) returns true for all elements Elem in List, otherwise false. The Pred function must return a boolean.

-spec any(Pred, List) -> boolean() when Pred :: fun((Elem :: T) -> boolean()), List :: [T], T :: term().

Returns true if Pred(Elem) returns true for at least one element Elem in List. The Pred function must return a boolean.

-spec append(ListOfLists) -> List1 when ListOfLists :: [List], List :: [T], List1 :: [T], T :: term().

Returns a list in which all the sublists of ListOfLists have been appended.

Example:

> lists:append([[1, 2, 3], [a, b], [4, 5, 6]]).
[1,2,3,a,b,4,5,6]

-spec append(List1, List2) -> List3 when List1 :: [T], List2 :: [T], List3 :: [T], T :: term().

Returns a new list List3, which is made from the elements of List1 followed by the elements of List2.

Example:

> lists:append("abc", "def").
"abcdef"

lists:append(A, B) is equivalent to A ++ B.

-spec concat(Things) -> string()
          when Things :: [Thing], Thing :: atom() | integer() | float() | string().

Concatenates the text representation of the elements of Things. The elements of Things can be atoms, integers, floats, or strings.

Example:

> lists:concat([doc, '/', file, '.', 3]).
"doc/file.3"

-spec delete(Elem, List1) -> List2 when Elem :: T, List1 :: [T], List2 :: [T], T :: term().

Returns a copy of List1 where the first element matching Elem is deleted, if there is such an element.

-spec droplast(List) -> InitList when List :: [T, ...], InitList :: [T], T :: term().

Drops the last element of a List. The list is to be non-empty, otherwise the function crashes with a function_clause.

-spec dropwhile(Pred, List1) -> List2
             when Pred :: fun((Elem :: T) -> boolean()), List1 :: [T], List2 :: [T], T :: term().

Drops elements Elem from List1 while Pred(Elem) returns true and returns the remaining list. The Pred function must return a boolean.

-spec duplicate(N, Elem) -> List when N :: non_neg_integer(), Elem :: T, List :: [T], T :: term().

Returns a list containing N copies of term Elem.

Example:

> lists:duplicate(5, xx).
[xx,xx,xx,xx,xx]

-spec enumerate(List1) -> List2
             when List1 :: [T], List2 :: [{Index, T}], Index :: integer(), T :: term().

Equivalent to enumerate(1, 1, List1).

-spec enumerate(Index, List1) -> List2
             when List1 :: [T], List2 :: [{Index, T}], Index :: integer(), T :: term().

Equivalent to enumerate(Index, 1, List1).

-spec enumerate(Index, Step, List1) -> List2
             when
                 List1 :: [T],
                 List2 :: [{Index, T}],
                 Index :: integer(),
                 Step :: integer(),
                 T :: term().

Returns List1 with each element H replaced by a tuple of form {I, H} where I is the position of H in List1. The enumeration starts with Index and increases by Step in each step.

That is, enumerate/3 behaves as if it had been defined as follows:

enumerate(I, S, List) ->
  {List1, _ } = lists:mapfoldl(fun(T, Acc) -> {{Acc, T}, Acc+S} end, I, List),
  List1.

The default values for Index and Step are both 1.

Examples:

> lists:enumerate([a,b,c]).
[{1,a},{2,b},{3,c}]

> lists:enumerate(10, [a,b,c]).
[{10,a},{11,b},{12,c}]

> lists:enumerate(0, -2, [a,b,c]).
[{0,a},{-2,b},{-4,c}]

-spec filter(Pred, List1) -> List2
          when Pred :: fun((Elem :: T) -> boolean()), List1 :: [T], List2 :: [T], T :: term().

List2 is a list of all elements Elem in List1 for which Pred(Elem) returns true. The Pred function must return a boolean.

-spec filtermap(Fun, List1) -> List2
             when
                 Fun :: fun((Elem) -> boolean() | {true, Value}),
                 List1 :: [Elem],
                 List2 :: [Elem | Value],
                 Elem :: term(),
                 Value :: term().

Calls Fun(Elem) on successive elements Elem of List1 in order to update or remove elements from List1.

Fun/1 must return either a Boolean or a tuple {true, Value}. The function returns the list of elements for which Fun returns a new value, where a value of true is synonymous with {true, Elem}.

That is, filtermap behaves as if it had been defined as follows:

filtermap(Fun, List1) ->
    lists:foldr(fun(Elem, Acc) ->
                       case Fun(Elem) of
                           false -> Acc;
                           true -> [Elem|Acc];
                           {true,Value} -> [Value|Acc]
                       end
                end, [], List1).

Example:

> lists:filtermap(fun(X) -> case X rem 2 of 0 -> {true, X div 2}; _ -> false end end, [1,2,3,4,5]).
[1,2]

-spec flatlength(DeepList) -> non_neg_integer() when DeepList :: [term() | DeepList].

Equivalent to length(flatten(DeepList)), but more efficient.

-spec flatmap(Fun, List1) -> List2
           when Fun :: fun((A) -> [B]), List1 :: [A], List2 :: [B], A :: term(), B :: term().

Takes a function from As to lists of Bs, and a list of As (List1) and produces a list of Bs by applying the function to every element in List1 and appending the resulting lists.

That is, flatmap behaves as if it had been defined as follows:

flatmap(Fun, List1) ->
    append(map(Fun, List1)).

Example:

> lists:flatmap(fun(X)->[X,X] end, [a,b,c]).
[a,a,b,b,c,c]

-spec flatten(DeepList) -> List when DeepList :: [term() | DeepList], List :: [term()].

Returns a flattened version of DeepList.

-spec flatten(DeepList, Tail) -> List
           when DeepList :: [term() | DeepList], Tail :: [term()], List :: [term()].

Returns a flattened version of DeepList with tail Tail appended.

-spec foldl(Fun, Acc0, List) -> Acc1
         when
             Fun :: fun((Elem :: T, AccIn) -> AccOut),
             Acc0 :: term(),
             Acc1 :: term(),
             AccIn :: term(),
             AccOut :: term(),
             List :: [T],
             T :: term().

Calls Fun(Elem, AccIn) on successive elements A of List, starting with AccIn == Acc0. Fun/2 must return a new accumulator, which is passed to the next call. The function returns the final value of the accumulator. Acc0 is returned if the list is empty.

Example:

> lists:foldl(fun(X, Sum) -> X + Sum end, 0, [1,2,3,4,5]).
15
> lists:foldl(fun(X, Prod) -> X * Prod end, 1, [1,2,3,4,5]).
120

-spec foldr(Fun, Acc0, List) -> Acc1
         when
             Fun :: fun((Elem :: T, AccIn) -> AccOut),
             Acc0 :: term(),
             Acc1 :: term(),
             AccIn :: term(),
             AccOut :: term(),
             List :: [T],
             T :: term().

Like foldl/3, but the list is traversed from right to left.

Example:

> P = fun(A, AccIn) -> io:format("~p ", [A]), AccIn end.
#Fun<erl_eval.12.2225172>
> lists:foldl(P, void, [1,2,3]).
1 2 3 void
> lists:foldr(P, void, [1,2,3]).
3 2 1 void

foldl/3 is tail recursive and is usually preferred to foldr/3.

-spec foreach(Fun, List) -> ok when Fun :: fun((Elem :: T) -> term()), List :: [T], T :: term().

Calls Fun(Elem) for each element Elem in List. This function is used for its side effects and the evaluation order is defined to be the same as the order of the elements in the list.

-spec join(Sep, List1) -> List2 when Sep :: T, List1 :: [T], List2 :: [T], T :: term().

Inserts Sep between each element in List1. Has no effect on the empty list and on a singleton list. For example:

> lists:join(x, [a,b,c]).
[a,x,b,x,c]
> lists:join(x, [a]).
[a]
> lists:join(x, []).
[]

-spec keydelete(Key, N, TupleList1) -> TupleList2
             when
                 Key :: term(),
                 N :: pos_integer(),
                 TupleList1 :: [Tuple],
                 TupleList2 :: [Tuple],
                 Tuple :: tuple().

Returns a copy of TupleList1 where the first occurrence of a tuple whose Nth element compares equal to Key is deleted, if there is such a tuple.

-spec keyfind(Key, N, TupleList) -> Tuple | false
           when Key :: term(), N :: pos_integer(), TupleList :: [Tuple], Tuple :: tuple().

Searches the list of tuples TupleList for a tuple whose Nth element compares equal to Key. Returns Tuple if such a tuple is found, otherwise false.

-spec keymap(Fun, N, TupleList1) -> TupleList2
          when
              Fun :: fun((Term1 :: term()) -> Term2 :: term()),
              N :: pos_integer(),
              TupleList1 :: [Tuple],
              TupleList2 :: [Tuple],
              Tuple :: tuple().

Returns a list of tuples where, for each tuple in TupleList1, the Nth element Term1 of the tuple has been replaced with the result of calling Fun(Term1).

Examples:

> Fun = fun(Atom) -> atom_to_list(Atom) end.
#Fun<erl_eval.6.10732646>
2> lists:keymap(Fun, 2, [{name,jane,22},{name,lizzie,20},{name,lydia,15}]).
[{name,"jane",22},{name,"lizzie",20},{name,"lydia",15}]

-spec keymember(Key, N, TupleList) -> boolean()
             when Key :: term(), N :: pos_integer(), TupleList :: [Tuple], Tuple :: tuple().

Returns true if there is a tuple in TupleList whose Nth element compares equal to Key, otherwise false.

-spec keymerge(N, TupleList1, TupleList2) -> TupleList3
            when
                N :: pos_integer(),
                TupleList1 :: [T1],
                TupleList2 :: [T2],
                TupleList3 :: [T1 | T2],
                T1 :: Tuple,
                T2 :: Tuple,
                Tuple :: tuple().

Returns the sorted list formed by merging TupleList1 and TupleList2.

The merge is performed on the Nth element of each tuple. Both TupleList1 and TupleList2 must be key-sorted before evaluating this function. When two tuples compare equal, the tuple from TupleList1 is picked before the tuple from TupleList2.

-spec keyreplace(Key, N, TupleList1, NewTuple) -> TupleList2
              when
                  Key :: term(),
                  N :: pos_integer(),
                  TupleList1 :: [Tuple],
                  TupleList2 :: [Tuple],
                  NewTuple :: Tuple,
                  Tuple :: tuple().

Returns a copy of TupleList1 where the first occurrence of a T tuple whose Nth element compares equal to Key is replaced with NewTuple, if there is such a tuple T.

-spec keysearch(Key, N, TupleList) -> {value, Tuple} | false
             when Key :: term(), N :: pos_integer(), TupleList :: [Tuple], Tuple :: tuple().

Searches the list of tuples TupleList for a tuple whose Nth element compares equal to Key. Returns {value, Tuple} if such a tuple is found, otherwise false.

Note

This function is retained for backward compatibility. Function keyfind/3 is usually more convenient.

-spec keysort(N, TupleList1) -> TupleList2
           when N :: pos_integer(), TupleList1 :: [Tuple], TupleList2 :: [Tuple], Tuple :: tuple().

Returns a list containing the sorted elements of list TupleList1. Sorting is performed on the Nth element of the tuples. The sort is stable.

-spec keystore(Key, N, TupleList1, NewTuple) -> TupleList2
            when
                Key :: term(),
                N :: pos_integer(),
                TupleList1 :: [Tuple],
                TupleList2 :: [Tuple, ...],
                NewTuple :: Tuple,
                Tuple :: tuple().

Returns a copy of TupleList1 where the first occurrence of a tuple T whose Nth element compares equal to Key is replaced with NewTuple, if there is such a tuple T. If there is no such tuple T, a copy of TupleList1 where [NewTuple] has been appended to the end is returned.

-spec keytake(Key, N, TupleList1) -> {value, Tuple, TupleList2} | false
           when
               Key :: term(),
               N :: pos_integer(),
               TupleList1 :: [tuple()],
               TupleList2 :: [tuple()],
               Tuple :: tuple().

Searches the list of tuples TupleList1 for a tuple whose Nth element compares equal to Key. Returns {value, Tuple, TupleList2} if such a tuple is found, otherwise false. TupleList2 is a copy of TupleList1 where the first occurrence of Tuple has been removed.

-spec last(List) -> Last when List :: [T, ...], Last :: T, T :: term().

Returns the last element in List.

-spec map(Fun, List1) -> List2
       when Fun :: fun((A) -> B), List1 :: [A], List2 :: [B], A :: term(), B :: term().

Takes a function from As to Bs, and a list of As and produces a list of Bs by applying the function to every element in the list. This function is used to obtain the return values. The evaluation order depends on the implementation.

-spec mapfoldl(Fun, Acc0, List1) -> {List2, Acc1}
            when
                Fun :: fun((A, AccIn) -> {B, AccOut}),
                Acc0 :: term(),
                Acc1 :: term(),
                AccIn :: term(),
                AccOut :: term(),
                List1 :: [A],
                List2 :: [B],
                A :: term(),
                B :: term().

Combines the operations of map/2 and foldl/3 into one pass.

Example:

Summing the elements in a list and double them at the same time:

> lists:mapfoldl(fun(X, Sum) -> {2*X, X+Sum} end,
0, [1,2,3,4,5]).
{[2,4,6,8,10],15}

-spec mapfoldr(Fun, Acc0, List1) -> {List2, Acc1}
            when
                Fun :: fun((A, AccIn) -> {B, AccOut}),
                Acc0 :: term(),
                Acc1 :: term(),
                AccIn :: term(),
                AccOut :: term(),
                List1 :: [A],
                List2 :: [B],
                A :: term(),
                B :: term().

Combines the operations of map/2 and foldr/3 into one pass.

-spec max(List) -> Max when List :: [T, ...], Max :: T, T :: term().

Returns the first element of List that compares greater than or equal to all other elements of List.

-spec member(Elem, List) -> boolean() when Elem :: T, List :: [T], T :: term().

Returns true if Elem matches some element of List, otherwise false.

-spec merge3(List1, List2, List3) -> List4
          when
              List1 :: [X],
              List2 :: [Y],
              List3 :: [Z],
              List4 :: [X | Y | Z],
              X :: term(),
              Y :: term(),
              Z :: term().

Returns the sorted list formed by merging List1, List2, and List3. All of List1, List2, and List3 must be sorted before evaluating this function.

When two elements compare equal, the element from List1, if there is such an element, is picked before the other element, otherwise the element from List2 is picked before the element from List3.

-spec merge(ListOfLists) -> List1 when ListOfLists :: [List], List :: [T], List1 :: [T], T :: term().

Returns the sorted list formed by merging all the sublists of ListOfLists. All sublists must be sorted before evaluating this function.

When two elements compare equal, the element from the sublist with the lowest position in ListOfLists is picked before the other element.

-spec merge(List1, List2) -> List3
         when List1 :: [X], List2 :: [Y], List3 :: [X | Y], X :: term(), Y :: term().

Returns the sorted list formed by merging List1 and List2. Both List1 and List2 must be sorted before evaluating this function.

When two elements compare equal, the element from List1 is picked before the element from List2.

-spec merge(Fun, List1, List2) -> List3
         when
             Fun :: fun((A, B) -> boolean()),
             List1 :: [A],
             List2 :: [B],
             List3 :: [A | B],
             A :: term(),
             B :: term().

Returns the sorted list formed by merging List1 and List2. Both List1 and List2 must be sorted according to the ordering function Fun before evaluating this function.

Fun(A, B) is to return true if A compares less than or equal to B in the ordering, otherwise false. When two elements compare equal, the element from List1 is picked before the element from List2.

-spec min(List) -> Min when List :: [T, ...], Min :: T, T :: term().

Returns the first element of List that compares less than or equal to all other elements of List.

-spec nth(N, List) -> Elem when N :: pos_integer(), List :: [T, ...], Elem :: T, T :: term().

Returns the Nth element of List.

Example:

> lists:nth(3, [a, b, c, d, e]).
c

-spec nthtail(N, List) -> Tail when N :: non_neg_integer(), List :: [T, ...], Tail :: [T], T :: term().

Returns the Nth tail of List, that is, the sublist of List starting at N+1 and continuing up to the end of the list.

Example

> lists:nthtail(3, [a, b, c, d, e]).
[d,e]
> tl(tl(tl([a, b, c, d, e]))).
[d,e]
> lists:nthtail(0, [a, b, c, d, e]).
[a,b,c,d,e]
> lists:nthtail(5, [a, b, c, d, e]).
[]

-spec partition(Pred, List) -> {Satisfying, NotSatisfying}
             when
                 Pred :: fun((Elem :: T) -> boolean()),
                 List :: [T],
                 Satisfying :: [T],
                 NotSatisfying :: [T],
                 T :: term().

Partitions List into two lists, where the first list contains all elements for which Pred(Elem) returns true, and the second list contains all elements for which Pred(Elem) returns false.

Examples:

> lists:partition(fun(A) -> A rem 2 == 1 end, [1,2,3,4,5,6,7]).
{[1,3,5,7],[2,4,6]}
> lists:partition(fun(A) -> is_atom(A) end, [a,b,1,c,d,2,3,4,e]).
{[a,b,c,d,e],[1,2,3,4]}

For a different way to partition a list, see splitwith/2.

-spec prefix(List1, List2) -> boolean() when List1 :: [T], List2 :: [T], T :: term().

Returns true if List1 is a prefix of List2, otherwise false.

-spec reverse(List1) -> List2 when List1 :: [T], List2 :: [T], T :: term().

Returns a list with the elements in List1 in reverse order.

-spec reverse(List1, Tail) -> List2 when List1 :: [T], Tail :: term(), List2 :: [T], T :: term().

Returns a list with the elements in List1 in reverse order, with tail Tail appended.

Example:

> lists:reverse([1, 2, 3, 4], [a, b, c]).
[4,3,2,1,a,b,c]

-spec search(Pred, List) -> {value, Value} | false
          when Pred :: fun((T) -> boolean()), List :: [T], Value :: T.

If there is a Value in List such that Pred(Value) returns true, returns {value, Value} for the first such Value, otherwise returns false. The Pred function must return a boolean.

-spec seq(From, To) -> Seq when From :: integer(), To :: integer(), Seq :: [integer()].

Equivalent to seq(From, To, 1).

-spec seq(From, To, Incr) -> Seq
       when From :: integer(), To :: integer(), Incr :: integer(), Seq :: [integer()].

Returns a sequence of integers that starts with From and contains the successive results of adding Incr to the previous element, until To is reached or passed (in the latter case, To is not an element of the sequence). Incr defaults to 1.

Failures:

• If To < From - Incr and Incr > 0.
• If To > From - Incr and Incr < 0.
• If Incr =:= 0 and From =/= To.

The following equalities hold for all sequences:

length(lists:seq(From, To)) =:= To - From + 1
length(lists:seq(From, To, Incr)) =:= (To - From + Incr) div Incr

Examples:

> lists:seq(1, 10).
[1,2,3,4,5,6,7,8,9,10]
> lists:seq(1, 20, 3).
[1,4,7,10,13,16,19]
> lists:seq(1, 0, 1).
[]
> lists:seq(10, 6, 4).
[]
> lists:seq(1, 1, 0).
[1]

-spec sort(List1) -> List2 when List1 :: [T], List2 :: [T], T :: term().

Returns a list containing the sorted elements of List1.

-spec sort(Fun, List1) -> List2
        when Fun :: fun((A :: T, B :: T) -> boolean()), List1 :: [T], List2 :: [T], T :: term().

Returns a list containing the sorted elements of List1, according to the ordering function Fun. Fun(A, B) is to return true if A compares less than or equal to B in the ordering, otherwise false.

-spec split(N, List1) -> {List2, List3}
         when N :: non_neg_integer(), List1 :: [T], List2 :: [T], List3 :: [T], T :: term().

Splits List1 into List2 and List3. List2 contains the first N elements and List3 the remaining elements (the Nth tail).

-spec splitwith(Pred, List) -> {List1, List2}
             when
                 Pred :: fun((T) -> boolean()),
                 List :: [T],
                 List1 :: [T],
                 List2 :: [T],
                 T :: term().

Partitions List into two lists according to Pred. splitwith/2 behaves as if it is defined as follows:

splitwith(Pred, List) ->
    {takewhile(Pred, List), dropwhile(Pred, List)}.

Examples:

> lists:splitwith(fun(A) -> A rem 2 == 1 end, [1,2,3,4,5,6,7]).
{[1],[2,3,4,5,6,7]}
> lists:splitwith(fun(A) -> is_atom(A) end, [a,b,1,c,d,2,3,4,e]).
{[a,b],[1,c,d,2,3,4,e]}

The Pred function must return a boolean. For a different way to partition a list, see partition/2.

-spec sublist(List1, Len) -> List2
           when List1 :: [T], List2 :: [T], Len :: non_neg_integer(), T :: term().

Returns the sublist of List1 starting at position 1 and with (maximum) Len elements. It is not an error for Len to exceed the length of the list, in that case the whole list is returned.

-spec sublist(List1, Start, Len) -> List2
           when
               List1 :: [T],
               List2 :: [T],
               Start :: pos_integer(),
               Len :: non_neg_integer(),
               T :: term().

Returns the sublist of List1 starting at Start and with (maximum) Len elements. It is not an error for Start+Len to exceed the length of the list.

Examples:

> lists:sublist([1,2,3,4], 2, 2).
[2,3]
> lists:sublist([1,2,3,4], 2, 5).
[2,3,4]
> lists:sublist([1,2,3,4], 5, 2).
[]

-spec subtract(List1, List2) -> List3 when List1 :: [T], List2 :: [T], List3 :: [T], T :: term().

Returns a new list List3 that is a copy of List1, subjected to the following procedure: for each element in List2, its first occurrence in List1 is deleted.

Example:

> lists:subtract("123212", "212").
"312".

lists:subtract(A, B) is equivalent to A -- B.

-spec suffix(List1, List2) -> boolean() when List1 :: [T], List2 :: [T], T :: term().

Returns true if List1 is a suffix of List2, otherwise false.

-spec sum(List) -> number() when List :: [number()].

Returns the sum of the elements in List.

-spec takewhile(Pred, List1) -> List2
             when Pred :: fun((Elem :: T) -> boolean()), List1 :: [T], List2 :: [T], T :: term().

Takes elements Elem from List1 while Pred(Elem) returns true, that is, the function returns the longest prefix of the list for which all elements satisfy the predicate. The Pred function must return a boolean.

-spec ukeymerge(N, TupleList1, TupleList2) -> TupleList3
             when
                 N :: pos_integer(),
                 TupleList1 :: [T1],
                 TupleList2 :: [T2],
                 TupleList3 :: [T1 | T2],
                 T1 :: Tuple,
                 T2 :: Tuple,
                 Tuple :: tuple().

Returns the sorted list formed by merging TupleList1 and TupleList2. The merge is performed on the Nth element of each tuple. Both TupleList1 and TupleList2 must be key-sorted without duplicates before evaluating this function.

When two tuples compare equal, the tuple from TupleList1 is picked and the one from TupleList2 is deleted.

-spec ukeysort(N, TupleList1) -> TupleList2
            when
                N :: pos_integer(), TupleList1 :: [Tuple], TupleList2 :: [Tuple], Tuple :: tuple().

Returns a list containing the sorted elements of list TupleList1 where all except the first tuple of the tuples comparing equal have been deleted. Sorting is performed on the Nth element of the tuples.

-spec umerge3(List1, List2, List3) -> List4
           when
               List1 :: [X],
               List2 :: [Y],
               List3 :: [Z],
               List4 :: [X | Y | Z],
               X :: term(),
               Y :: term(),
               Z :: term().

Returns the sorted list formed by merging List1, List2, and List3. All of List1, List2, and List3 must be sorted and contain no duplicates before evaluating this function.

When two elements compare equal, the element from List1 is picked if there is such an element, otherwise the element from List2 is picked, and the other is deleted.

-spec umerge(ListOfLists) -> List1 when ListOfLists :: [List], List :: [T], List1 :: [T], T :: term().

Returns the sorted list formed by merging all the sublists of ListOfLists. All sublists must be sorted and contain no duplicates before evaluating this function.

When two elements compare equal, the element from the sublist with the lowest position in ListOfLists is picked and the other is deleted.

-spec umerge(List1, List2) -> List3
          when List1 :: [X], List2 :: [Y], List3 :: [X | Y], X :: term(), Y :: term().

Returns the sorted list formed by merging List1 and List2. Both List1 and List2 must be sorted and contain no duplicates before evaluating this function.

When two elements compare equal, the element from List1 is picked and the one from List2 is deleted.

-spec umerge(Fun, List1, List2) -> List3
          when
              Fun :: fun((A, B) -> boolean()),
              List1 :: [A],
              List2 :: [B],
              List3 :: [A | B],
              A :: term(),
              B :: term().

Returns the sorted list formed by merging List1 and List2. Both List1 and List2 must be sorted according to the ordering function Fun and contain no duplicates before evaluating this function.

Fun(A, B) is to return true if A compares less than or equal to B in the ordering, otherwise false. When two elements compare equal, the element from List1 is picked and the one from List2 is deleted.

-spec uniq(List1) -> List2 when List1 :: [T], List2 :: [T], T :: term().

Returns a list containing the elements of List1 with duplicated elements removed (preserving the order of the elements). The first occurrence of each element is kept.

Examples:

> lists:uniq([3,3,1,2,1,2,3]).
[3,1,2]
> lists:uniq([a, a, 1, b, 2, a, 3]).
[a, 1, b, 2, 3]

-spec uniq(Fun, List1) -> List2 when Fun :: fun((T) -> any()), List1 :: [T], List2 :: [T], T :: term().

Returns a list containing the elements of List1 without the elements for which Fun returned duplicate values (preserving the order of the elements). The first occurrence of each element is kept.

Examples:

> lists:uniq(fun({X, _}) -> X end, [{b, 2}, {a, 1}, {c, 3}, {a, 2}]).
[{b, 2}, {a, 1}, {c, 3}]

-spec unzip3(List1) -> {List2, List3, List4}
          when
              List1 :: [{A, B, C}],
              List2 :: [A],
              List3 :: [B],
              List4 :: [C],
              A :: term(),
              B :: term(),
              C :: term().

"Unzips" a list of three-tuples into three lists, where the first list contains the first element of each tuple, the second list contains the second element of each tuple, and the third list contains the third element of each tuple.

-spec unzip(List1) -> {List2, List3}
         when List1 :: [{A, B}], List2 :: [A], List3 :: [B], A :: term(), B :: term().

"Unzips" a list of two-tuples into two lists, where the first list contains the first element of each tuple, and the second list contains the second element of each tuple.

-spec usort(List1) -> List2 when List1 :: [T], List2 :: [T], T :: term().

Returns a list containing the sorted elements of List1 where all except the first element of the elements comparing equal have been deleted.

-spec usort(Fun, List1) -> List2
         when Fun :: fun((T, T) -> boolean()), List1 :: [T], List2 :: [T], T :: term().

Returns a list containing the sorted elements of List1 where all except the first element of the elements comparing equal according to the ordering function Fun have been deleted. Fun(A, B) is to return true if A compares less than or equal to B in the ordering, otherwise false.

-spec zip3(List1, List2, List3) -> List4
        when
            List1 :: [A],
            List2 :: [B],
            List3 :: [C],
            List4 :: [{A, B, C}],
            A :: term(),
            B :: term(),
            C :: term().

Equivalent to zip3(List1, List2, List3, fail).

-spec zip3(List1, List2, List3, How) -> List4
        when
            List1 :: [A],
            List2 :: [B],
            List3 :: [C],
            List4 :: [{A | DefaultA, B | DefaultB, C | DefaultC}],
            A :: term(),
            B :: term(),
            C :: term(),
            How :: fail | trim | {pad, {DefaultA, DefaultB, DefaultC}},
            DefaultA :: term(),
            DefaultB :: term(),
            DefaultC :: term().

"Zips" three lists into one list of three-tuples, where the first element of each tuple is taken from the first list, the second element is taken from the corresponding element in the second list, and the third element is taken from the corresponding element in the third list.

For a description of the How parameter, see zip/3.

-spec zip(List1, List2) -> List3
       when List1 :: [A], List2 :: [B], List3 :: [{A, B}], A :: term(), B :: term().

Equivalent to zip(List1, List2, fail).

-spec zip(List1, List2, How) -> List3
       when
           List1 :: [A],
           List2 :: [B],
           List3 :: [{A | DefaultA, B | DefaultB}],
           A :: term(),
           B :: term(),
           How :: fail | trim | {pad, {DefaultA, DefaultB}},
           DefaultA :: term(),
           DefaultB :: term().

"Zips" two lists into one list of two-tuples, where the first element of each tuple is taken from the first list and the second element is taken from the corresponding element in the second list.

The How parameter specifies the behavior if the given lists are of different lengths.

• fail - The call will fail if the given lists are not of equal length. This is the default.

• trim - Surplus elements from the longer list will be ignored.

  Examples:

  > lists:zip([a, b], [1, 2, 3], trim).
  [{a,1},{b,2}]
  > lists:zip([a, b, c], [1, 2], trim).
  [{a,1},{b,2}]

• {pad, Defaults} - The shorter list will be padded to the length of the longer list, using the respective elements from the given Defaults tuple.

  Examples:

  > lists:zip([a, b], [1, 2, 3], {pad, {x, 0}}).
  [{a,1},{b,2},{x,3}]
  > lists:zip([a, b, c], [1, 2], {pad, {x, 0}}).
  [{a,1},{b,2},{c,0}]

-spec zipwith3(Combine, List1, List2, List3) -> List4
            when
                Combine :: fun((X, Y, Z) -> T),
                List1 :: [X],
                List2 :: [Y],
                List3 :: [Z],
                List4 :: [T],
                X :: term(),
                Y :: term(),
                Z :: term(),
                T :: term().

Equivalent to zipwith3(Combine, List1, List2, List3, fail).

-spec zipwith3(Combine, List1, List2, List3, How) -> List4
            when
                Combine :: fun((X | DefaultX, Y | DefaultY, Z | DefaultZ) -> T),
                List1 :: [X],
                List2 :: [Y],
                List3 :: [Z],
                List4 :: [T],
                X :: term(),
                Y :: term(),
                Z :: term(),
                How :: fail | trim | {pad, {DefaultX, DefaultY, DefaultZ}},
                DefaultX :: term(),
                DefaultY :: term(),
                DefaultZ :: term(),
                T :: term().

Combines the elements of three lists into one list. For each triple X, Y, Z of list elements from the three lists, the element in the result list is Combine(X, Y, Z).

For a description of the How parameter, see zip/3.

zipwith3(fun(X, Y, Z) -> {X,Y,Z} end, List1, List2, List3) is equivalent to zip3(List1, List2, List3).

Examples:

> lists:zipwith3(fun(X, Y, Z) -> X+Y+Z end, [1,2,3], [4,5,6], [7,8,9]).
[12,15,18]
> lists:zipwith3(fun(X, Y, Z) -> [X,Y,Z] end, [a,b,c], [x,y,z], [1,2,3]).
[[a,x,1],[b,y,2],[c,z,3]]

-spec zipwith(Combine, List1, List2) -> List3
           when
               Combine :: fun((X, Y) -> T),
               List1 :: [X],
               List2 :: [Y],
               List3 :: [T],
               X :: term(),
               Y :: term(),
               T :: term().

Equivalent to zipwith(Combine, List1, List2, fail).

-spec zipwith(Combine, List1, List2, How) -> List3
           when
               Combine :: fun((X | DefaultX, Y | DefaultY) -> T),
               List1 :: [X],
               List2 :: [Y],
               List3 :: [T],
               X :: term(),
               Y :: term(),
               How :: fail | trim | {pad, {DefaultX, DefaultY}},
               DefaultX :: term(),
               DefaultY :: term(),
               T :: term().

Combines the elements of two lists into one list. For each pair X, Y of list elements from the two lists, the element in the result list is Combine(X, Y).

For a description of the How parameter, see zip/3.

zipwith(fun(X, Y) -> {X,Y} end, List1, List2) is equivalent to zip(List1, List2).

Example:

> lists:zipwith(fun(X, Y) -> X+Y end, [1,2,3], [4,5,6]).
[5,7,9]