# ordsets

## Functions for Manipulating Sets as Ordered Lists

Sets are collections of elements with no duplicate elements. An `ordset` is a representation of a set, where an ordered list is used to store the elements of the set. An ordered list is more efficient than an unordered list.

This module provides exactly the same interface as the module `sets` but with a defined representation. One difference is that while `sets` considers two elements as different if they do not match (`=:=`), this module considers two elements as different if and only if they do not compare equal (`==`).

As returned by new/0.

### new() -> []

Returns a new empty ordered set.

### is_set(Ordset) -> boolean()

Returns `true` if `Ordset` is an ordered set of elements, otherwise `false`.

### size(Ordset) -> integer() >= 0

Returns the number of elements in `Ordset`.

### to_list(Ordset) -> List

Returns the elements of `Ordset` as a list.

### from_list(List) -> Ordset

Returns an ordered set of the elements in `List`.

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

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

Returns a new ordered set formed from `Ordset1` with `Element` inserted.

### del_element(Element, Ordset1) -> Ordset2

Returns `Ordset1`, but with `Element` removed.

### union(Ordset1, Ordset2) -> Ordset3

Returns the merged (union) set of `Ordset1` and `Ordset2`.

### union(OrdsetList) -> Ordset

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

### intersection(Ordset1, Ordset2) -> Ordset3

Returns the intersection of `Ordset1` and `Ordset2`.

### intersection(OrdsetList) -> Ordset

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

### is_disjoint(Ordset1, Ordset2) -> boolean()

Returns `true` if `Ordset1` and `Ordset2` are disjoint (have no elements in common), and `false` otherwise.

### subtract(Ordset1, Ordset2) -> Ordset3

Returns only the elements of `Ordset1` which are not also elements of `Ordset2`.

### is_subset(Ordset1, Ordset2) -> boolean()

Returns `true` when every element of `Ordset1` is also a member of `Ordset2`, otherwise `false`.

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

Fold `Function` over every element in `Ordset` returning the final value of the accumulator.

### filter(Pred, Ordset1) -> Ordset2

Filter elements in `Ordset1` with boolean function `Pred`.