# sets

## Functions for Set Manipulation

Sets are collections of elements with no duplicate elements. The representation of a set is not defined.

This module provides exactly the same interface as the module
`ordsets`

but with a defined 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 (`==`

).

#### Functions

### new() -> set()

Returns a new empty set.

### is_set(Set) -> boolean()

`Set = term()`

Returns `true`

if

is a set of
elements, otherwise `false`

.

### to_list(Set) -> List

`Set = set(Element)`

`List = [Element]`

Returns the elements of

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

### is_element(Element, Set) -> boolean()

`Set = set(Element)`

Returns `true`

if

is an element of

, otherwise `false`

.

### add_element(Element, Set1) -> Set2

`Set1 = Set2 = set(Element)`

Returns a new set formed from

with

inserted.

### del_element(Element, Set1) -> Set2

`Set1 = Set2 = set(Element)`

Returns

, but with

removed.

### union(Set1, Set2) -> Set3

`Set1 = Set2 = Set3 = set(Element)`

Returns the merged (union) set of

and

.

### union(SetList) -> Set

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

### intersection(Set1, Set2) -> Set3

`Set1 = Set2 = Set3 = set(Element)`

Returns the intersection of

and

.

### intersection(SetList) -> Set

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

### is_disjoint(Set1, Set2) -> boolean()

`Set1 = Set2 = set(Element)`

Returns `true`

if

and

are disjoint (have no elements in common),
and `false`

otherwise.

### subtract(Set1, Set2) -> Set3

`Set1 = Set2 = Set3 = set(Element)`

Returns only the elements of

which are not
also elements of

.

### is_subset(Set1, Set2) -> boolean()

`Set1 = Set2 = set(Element)`

Returns `true`

when every element of

1 is
also a member of

, otherwise `false`

.

### fold(Function, Acc0, Set) -> Acc1

`Function = fun((Element, AccIn) -> AccOut)`

`Set = set(Element)`

`Acc0 = Acc1 = AccIn = AccOut = Acc`

Fold

over every element in

returning the final value of the accumulator.
The evaluation order is undefined.

### filter(Pred, Set1) -> Set2

`Pred = fun((Element) -> boolean())`

`Set1 = Set2 = set(Element)`

Filter elements in

with boolean function

.