sets(3)

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(3) 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}]).

COMPATIBILITY

The following functions in this module also exist and provide the same functionality in the gb_sets(3) and ordsets(3) modules. That is, by only changing the module name for each call, you can try out different set representations.

    *   add_element/2

    *   del_element/2

    *   filter/2

    *   filtermap/2

    *   fold/3

    *   from_list/1

    *   intersection/1

    *   intersection/2

    *   is_element/2

    *   is_empty/1

    *   is_equal/2

    *   is_set/1

    *   is_subset/2

    *   map/2

    *   new/0

    *   size/1

    *   subtract/2

    *   to_list/1

    *   union/1

    *   union/2

    Note:
While the three set implementations offer the same functionality with respect to the aforementioned functions, their overall behavior may differ. As mentioned, this module considers elements as different if and only if they do not match (=:=), while both ordsets and gb_sets consider elements as different if and only if they do not compare equal (==).

Example:

1> sets:is_element(1.0, sets:from_list([1])).
false
2> ordsets:is_element(1.0, ordsets:from_list([1])).
true
2> gb_sets:is_element(1.0, gb_sets:from_list([1])).
true

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.

filtermap(Fun, Set1) -> Set2

    Types:
        Fun = fun((Element1) -> boolean() | {true, Element2})
        Set1 = set(Element1)
        Set2 = set(Element1 | Element2)

    Filters and maps elements in Set1 with function Fun.

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_equal(Set1, Set2) -> boolean()

    Types:
        Set1 = Set2 = set()

    Returns true if Set1 and Set2 are equal, that is when every element of one set is also a member of the respective other 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.

map(Fun, Set1) -> Set2

    Types:
        Fun = fun((Element1) -> Element2)
        Set1 = set(Element1)
        Set2 = set(Element2)

    Maps elements in Set1 with mapping function Fun.

new() -> set(none())

    Returns a new empty set.

new(Opts :: [{version, 1..2}]) -> set(none())

    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(3), ordsets(3)