NAME

       sets - Functions for set manipulation.

DESCRIPTION

       Sets are collections of elements with no duplicate elements.

       The  data  representing  a  set  as  used by this module is to be regarded as opaque by other modules. In
       abstract terms, the representation is a composite type of existing Erlang terms. See note on data  types.
       Any code assuming knowledge of the format is running on thin ice.

       This module provides the same interface as the ordsets(3erl) module but with an undefined representation.
       One  difference is that while this module considers two elements as different if they do not match (=:=),
       ordsets considers two elements as different if and only if they do not compare equal (==).

       Erlang/OTP 24.0 introduced a new internal representation for sets which is  more  performant.  Developers
       can  use  this  new  representation  by  passing  the {version, 2} flag to new/1 and from_list/2, such as
       sets:new([{version, 2}]). This new representation will become the default in future Erlang/OTP  versions.
       Functions  that work on two sets, such as union/2 and similar, will work with sets of different versions.
       In such cases, there is no guarantee about the version of the returned set. Explicit conversion from  the
       old version to the new one can be done with sets:from_list(sets:to_list(Old), [{version,2}]).

DATA TYPES

       set(Element)

              As returned by new/0.

       set() = set(term())

EXPORTS

       add_element(Element, Set1) -> Set2

              Types:

                 Set1 = Set2 = set(Element)

              Returns a new set formed from Set1 with Element inserted.

       del_element(Element, Set1) -> Set2

              Types:

                 Set1 = Set2 = set(Element)

              Returns Set1, but with Element removed.

       filter(Pred, Set1) -> Set2

              Types:

                 Pred = fun((Element) -> boolean())
                 Set1 = Set2 = set(Element)

              Filters elements in Set1 with boolean function Pred.

       fold(Function, Acc0, Set) -> Acc1

              Types:

                 Function = fun((Element, AccIn) -> AccOut)
                 Set = set(Element)
                 Acc0 = Acc1 = AccIn = AccOut = Acc

              Folds  Function  over  every  element  in  Set and returns the final value of the accumulator. The
              evaluation order is undefined.

       from_list(List) -> Set

              Types:

                 List = [Element]
                 Set = set(Element)

              Returns a set of the elements in List.

       from_list(List, Opts :: [{version, 1..2}]) -> Set

              Types:

                 List = [Element]
                 Set = set(Element)

              Returns a set of the elements in List at the given version.

       intersection(SetList) -> Set

              Types:

                 SetList = [set(Element), ...]
                 Set = set(Element)

              Returns the intersection of the non-empty list of sets.

       intersection(Set1, Set2) -> Set3

              Types:

                 Set1 = Set2 = Set3 = set(Element)

              Returns the intersection of Set1 and Set2.

       is_disjoint(Set1, Set2) -> boolean()

              Types:

                 Set1 = Set2 = set(Element)

              Returns true if Set1 and Set2 are disjoint (have no elements in common), otherwise false.

       is_element(Element, Set) -> boolean()

              Types:

                 Set = set(Element)

              Returns true if Element is an element of Set, otherwise false.

       is_empty(Set) -> boolean()

              Types:

                 Set = set()

              Returns true if Set is an empty set, otherwise false.

       is_set(Set) -> boolean()

              Types:

                 Set = term()

              Returns true if Set appears to be a set of elements,  otherwise  false.  Note  that  the  test  is
              shallow  and  will  return true for any term that coincides with the possible representations of a
              set. See also note on data types.

       is_subset(Set1, Set2) -> boolean()

              Types:

                 Set1 = Set2 = set(Element)

              Returns true when every element of Set1 is also a member of Set2, otherwise false.

       new() -> set()

              Returns a new empty set.

       new(Opts :: [{version, 1..2}]) -> set()

              Returns a new empty set at the given version.

       size(Set) -> integer() >= 0

              Types:

                 Set = set()

              Returns the number of elements in Set.

       subtract(Set1, Set2) -> Set3

              Types:

                 Set1 = Set2 = Set3 = set(Element)

              Returns only the elements of Set1 that are not also elements of Set2.

       to_list(Set) -> List

              Types:

                 Set = set(Element)
                 List = [Element]

              Returns the elements of Set as a list. The order of the returned elements is undefined.

       union(SetList) -> Set

              Types:

                 SetList = [set(Element)]
                 Set = set(Element)

              Returns the merged (union) set of the list of sets.

       union(Set1, Set2) -> Set3

              Types:

                 Set1 = Set2 = Set3 = set(Element)

              Returns the merged (union) set of Set1 and Set2.

SEE ALSO

       gb_sets(3erl), ordsets(3erl)

Ericsson AB                                      stdlib 4.3.1.3                                       sets(3erl)