---
name: "ordsets"
section: "3erl"
platform: "linux"
package: "erlang-manpages"
version: "1:25.2.3+dfsg-1+deb12u4"
release: "Debian 12 (Bookworm)"
platforms: ["linux"]
url: "https://new.carta.tech/ordsets"
---

# ordsets(3erl)

Functions for manipulating sets as ordered lists.

## NAME

ordsets - Functions for manipulating sets as ordered lists.

## DESCRIPTION

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. Elements are ordered according to the *Erlang term order*.

This module provides the same interface as the *[sets(3erl)](/sets/3erl.md)* module 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 (*==*).

## DATA TYPES

```
ordset(T) = [T]
```

As returned by *new/0*.

## EXPORTS

```
add_element(Element, Ordset1) -> Ordset2
```

Types:

Element = E\
 Ordset1 = ordset(T)\
 Ordset2 = ordset(T \| E)\

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

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

Types:

Element = term()\
 Ordset1 = Ordset2 = ordset(T)\

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

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

Types:

Pred = fun((Element :: T) -\> boolean())\
 Ordset1 = Ordset2 = ordset(T)\

Filters elements in *Ordset1* with boolean function *Pred*.

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

Types:

Function = \
\
     fun((Element :: T, AccIn :: term()) -\> AccOut :: term())\
 Ordset = ordset(T)\
 Acc0 = Acc1 = term()\

Folds *Function* over every element in *Ordset* and returns the final value of the accumulator.

```
from_list(List) -> Ordset
```

Types:

List = \[T\]\
 Ordset = ordset(T)\

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

```
intersection(OrdsetList) -> Ordset
```

Types:

OrdsetList = \[ordset(term()), ...\]\
 Ordset = ordset(term())\

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

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

Types:

Ordset1 = Ordset2 = Ordset3 = ordset(term())\

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

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

Types:

Ordset1 = Ordset2 = ordset(term())\

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

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

Types:

Element = term()\
 Ordset = ordset(term())\

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

```
is_empty(Ordset) -> boolean()
```

Types:

Ordset = ordset(term())\

Returns *true* if *Ordset* is an empty set, otherwise *false*.

```
is_set(Ordset) -> boolean()
```

Types:

Ordset = term()\

Returns *true* if *Ordset* is an ordered set of elements, otherwise *false*. This function will return *true* for any ordered list, even when not constructed by the functions in this module.

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

Types:

Ordset1 = Ordset2 = ordset(term())\

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

```
new() -> []
```

Returns a new empty ordered set.

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

Types:

Ordset = ordset(term())\

Returns the number of elements in *Ordset*.

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

Types:

Ordset1 = Ordset2 = Ordset3 = ordset(term())\

Returns only the elements of *Ordset1* that are not also elements of *Ordset2*.

```
to_list(Ordset) -> List
```

Types:

Ordset = ordset(T)\
 List = \[T\]\

Returns the elements of *Ordset* as a list.

```
union(OrdsetList) -> Ordset
```

Types:

OrdsetList = \[ordset(T)\]\
 Ordset = ordset(T)\

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

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

Types:

Ordset1 = ordset(T1)\
 Ordset2 = ordset(T2)\
 Ordset3 = ordset(T1 \| T2)\

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

## SEE ALSO

*[gb\_sets(3erl)](/gb_sets/3erl.md)*, *[sets(3erl)](/sets/3erl.md)*