# Types

## Set

opaque </>

A set is a collection of unique members of the same type.

It is implemented using the `gleam/dict` module, so inserts and lookups have logarithmic time complexity.

``pub opaque type Set(member)``

# Functions

## contains

</>
``pub fn contains(in set: Set(a), this member: a) -> Bool``

Checks whether a set contains a given member.

This function runs in logarithmic time.

## Examples

``````new()
|> insert(2)
|> contains(2)
// -> True
``````
``````new()
|> insert(2)
|> contains(1)
// -> False
``````

## delete

</>
``pub fn delete(from set: Set(a), this member: a) -> Set(a)``

Removes a member from a set. If the set does not contain the member then the set is returned unchanged.

This function runs in logarithmic time.

## Examples

``````new()
|> insert(2)
|> delete(2)
|> contains(1)
// -> False
``````

## difference

</>
``````pub fn difference(
from first: Set(a),
minus second: Set(a),
) -> Set(a)``````

Creates a new set that contains members that are present in the first set but not the second.

## Examples

``````difference(from_list([1, 2]), from_list([2, 3, 4])) |> to_list
// -> [1]
``````

## drop

</>
``pub fn drop(from set: Set(a), drop disallowed: List(a)) -> Set(a)``

Creates a new set from a given set with all the same entries except any entry found on the given list.

## Examples

``````drop(from_list([1, 2, 3, 4]), [1, 3])
// -> [2, 4]
``````

## filter

</>
``````pub fn filter(
in set: Set(a),
keeping predicate: fn(a) -> Bool,
) -> Set(a)``````

Creates a new set from an existing set, minus any members that a given function returns `False` for.

This function runs in loglinear time.

## Examples

``````import gleam/int

from_list([1, 4, 6, 3, 675, 44, 67])
|> filter(for: int.is_even)
|> to_list
// -> [4, 6, 44]
``````

## fold

</>
``````pub fn fold(
over set: Set(a),
from initial: b,
with reducer: fn(b, a) -> b,
) -> b``````

Combines all entries into a single value by calling a given function on each one.

Sets are not ordered so the values are not returned in any specific order. Do not write code that relies on the order entries are used by this function as it may change in later versions of Gleam or Erlang.

# Examples

``````from_list([1, 3, 9])
|> fold(0, fn(accumulator, member) { accumulator + member })
// -> 13
``````

## from_list

</>
``pub fn from_list(members: List(a)) -> Set(a)``

Creates a new set of the members in a given list.

This function runs in loglinear time.

## Examples

``````import gleam/int
import gleam/list

[1, 1, 2, 4, 3, 2] |> from_list |> to_list |> list.sort(by: int.compare)
// -> [1, 2, 3, 4]
``````

## insert

</>
``pub fn insert(into set: Set(a), this member: a) -> Set(a)``

Inserts an member into the set.

This function runs in logarithmic time.

## Examples

``````new()
|> insert(1)
|> insert(2)
|> size
// -> 2
``````

## intersection

</>
``````pub fn intersection(
of first: Set(a),
and second: Set(a),
) -> Set(a)``````

Creates a new set that contains members that are present in both given sets.

This function runs in loglinear time.

## Examples

``````intersection(from_list([1, 2]), from_list([2, 3])) |> to_list
// -> [2]
``````

## is_disjoint

</>
``pub fn is_disjoint(first: Set(a), from second: Set(a)) -> Bool``

Determines if two sets contain no common members

## Examples

``````is_disjoint(from_list([1, 2, 3], from_list([4, 5, 6])))
// -> True
``````
``````is_disjoint(from_list([1, 2, 3]), from_list([3, 4, 5]))
// -> False
``````

## is_empty

</>
``pub fn is_empty(set: Set(a)) -> Bool``

Determines whether or not the set is empty.

## Examples

``````new() |> is_empty
// -> True
``````
``````new() |> insert(1) |> is_empty
// -> False
``````

## is_subset

</>
``pub fn is_subset(first: Set(a), of second: Set(a)) -> Bool``

Determines if a set is fully contained by another.

## Examples

``````is_subset(from_list([1]), from_list([1, 2]))
// -> True
``````
``````is_subset(from_list([1, 2, 3]), from_list([3, 4, 5]))
// -> False
``````

## map

</>
``pub fn map(set: Set(a), with fun: fn(a) -> b) -> Set(b)``

Creates a new set from a given set with the result of applying the given function to each member.

## Examples

``````map(from_list([1, 2, 3, 4], fn(x) { x * 2 }))
// -> [2, 4, 6, 8]
``````

## new

</>
``pub fn new() -> Set(a)``

Creates a new empty set.

## size

</>
``pub fn size(set: Set(a)) -> Int``

Gets the number of members in a set.

This function runs in constant time.

## Examples

``````new()
|> insert(1)
|> insert(2)
|> size
// -> 2
``````

## symmetric_difference

</>
``````pub fn symmetric_difference(
of first: Set(a),
and second: Set(a),
) -> Set(a)``````

Creates a new set that contains members that are present in either set, but not both.

``````symmetric_difference(from_list([1, 2, 3]), from_list([3, 4])) |> to_list
// -> [1, 2, 4]
``````

## take

</>
``pub fn take(from set: Set(a), keeping desired: List(a)) -> Set(a)``

Creates a new set from a given set, only including any members which are in a given list.

This function runs in loglinear time.

## Examples

``````from_list([1, 2, 3])
|> take([1, 3, 5])
|> to_list
// -> [1, 3]
``````

## to_list

</>
``pub fn to_list(set: Set(a)) -> List(a)``

Converts the set into a list of the contained members.

The list has no specific ordering, any unintentional ordering may change in future versions of Gleam or Erlang.

This function runs in linear time.

## Examples

``````new() |> insert(2) |> to_list
// -> [2]
``````

## union

</>
``pub fn union(of first: Set(a), and second: Set(a)) -> Set(a)``

Creates a new set that contains all members of both given sets.

This function runs in loglinear time.

## Examples

``````union(from_list([1, 2]), from_list([2, 3])) |> to_list
// -> [1, 2, 3]
``````