View Source sets (stdlib v6.0)

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 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 and ordsets 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

Summary

Types

set()

set(Element)

As returned by new/0.

Functions

add_element(Element, Set1)

Returns a new set formed from Set1 with Element inserted.

del_element(Element, Set1)

Returns Set1, but with Element removed.

filter(Pred, Set1)

Filters elements in Set1 with boolean function Pred.

filtermap(Fun, Set1)

Filters and maps elements in Set1 with function Fun.

fold(Function, Acc0, Set)

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

from_list(List)

Returns a set of the elements in List.

from_list/2

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

intersection(SetList)

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

intersection(Set1, Set2)

Returns the intersection of Set1 and Set2.

is_disjoint(Set1, Set2)

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

is_element(Element, Set)

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

is_empty(Set)

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

is_equal(Set1, Set2)

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)

Returns true if Set appears to be a set of elements, otherwise false.

is_subset(Set1, Set2)

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

map(Fun, Set1)

Maps elements in Set1 with mapping function Fun.

new()

Returns a new empty set.

new/1

Returns a new empty set at the given version.

size(Set)

Returns the number of elements in Set.

subtract(Set1, Set2)

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

to_list(Set)

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

union(SetList)

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

union(Set1, Set2)

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

Types

set()

-type set() :: set(_).

set(Element)

-opaque set(Element)

As returned by new/0.

Functions

add_element(Element, Set1)

-spec add_element(Element, Set1) -> Set2 when Set1 :: set(Element), Set2 :: set(Element).

Returns a new set formed from Set1 with Element inserted.

del_element(Element, Set1)

-spec del_element(Element, Set1) -> Set2 when Set1 :: set(Element), Set2 :: set(Element).

Returns Set1, but with Element removed.

filter(Pred, Set1)

-spec filter(Pred, Set1) -> Set2
                when Pred :: fun((Element) -> boolean()), Set1 :: set(Element), Set2 :: set(Element).

Filters elements in Set1 with boolean function Pred.

filtermap(Fun, Set1)

(since OTP 27.0)

-spec filtermap(Fun, Set1) -> Set2
                   when
                       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)

-spec fold(Function, Acc0, Set) -> Acc1
              when
                  Function :: fun((Element, AccIn) -> AccOut),
                  Set :: set(Element),
                  Acc0 :: Acc,
                  Acc1 :: Acc,
                  AccIn :: Acc,
                  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)

-spec from_list(List) -> Set when List :: [Element], Set :: set(Element).

Returns a set of the elements in List.

from_list/2

(since OTP 24.0)

-spec from_list(List, [{version, 1..2}]) -> Set when List :: [Element], Set :: set(Element).

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

intersection(SetList)

-spec intersection(SetList) -> Set when SetList :: [set(Element), ...], Set :: set(Element).

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

intersection(Set1, Set2)

-spec intersection(Set1, Set2) -> Set3
                      when Set1 :: set(Element), Set2 :: set(Element), Set3 :: set(Element).

Returns the intersection of Set1 and Set2.

is_disjoint(Set1, Set2)

-spec is_disjoint(Set1, Set2) -> boolean() when Set1 :: set(Element), Set2 :: set(Element).

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

is_element(Element, Set)

-spec is_element(Element, Set) -> boolean() when Set :: set(Element).

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

is_empty(Set)

(since OTP 21.0)

-spec is_empty(Set) -> boolean() when Set :: set().

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

is_equal(Set1, Set2)

(since OTP 27.0)

-spec is_equal(Set1, Set2) -> boolean() when Set1 :: set(), 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)

-spec is_set(Set) -> boolean() when 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)

-spec is_subset(Set1, Set2) -> boolean() when Set1 :: set(Element), Set2 :: set(Element).

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

map(Fun, Set1)

(since OTP 27.0)

-spec map(Fun, Set1) -> Set2
             when Fun :: fun((Element1) -> Element2), Set1 :: set(Element1), Set2 :: set(Element2).

Maps elements in Set1 with mapping function Fun.

new()

-spec new() -> set(none()).

Returns a new empty set.

new/1

(since OTP 24.0)

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

Returns a new empty set at the given version.

size(Set)

-spec size(Set) -> non_neg_integer() when Set :: set().

Returns the number of elements in Set.

subtract(Set1, Set2)

-spec subtract(Set1, Set2) -> Set3 when Set1 :: set(Element), Set2 :: set(Element), Set3 :: set(Element).

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

to_list(Set)

-spec to_list(Set) -> List when Set :: set(Element), List :: [Element].

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

union(SetList)

-spec union(SetList) -> Set when SetList :: [set(Element)], Set :: set(Element).

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

union(Set1, Set2)

-spec union(Set1, Set2) -> Set3 when Set1 :: set(Element), Set2 :: set(Element), Set3 :: set(Element).

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

View Source sets (stdlib v6.0)

Compatibility

Note

See Also

Summary

Types

Functions

Types

set()

set(Element)

Functions

add_element(Element, Set1)

del_element(Element, Set1)

filter(Pred, Set1)

filtermap(Fun, Set1)

fold(Function, Acc0, Set)

from_list(List)

from_list/2

intersection(SetList)

intersection(Set1, Set2)

is_disjoint(Set1, Set2)

is_element(Element, Set)

is_empty(Set)

is_equal(Set1, Set2)

is_set(Set)

is_subset(Set1, Set2)

map(Fun, Set1)

new()

new/1

size(Set)

subtract(Set1, Set2)

to_list(Set)

union(SetList)

union(Set1, Set2)