GAP (datastructures) - Chapter 8: Hashsets

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8 Hashsets
8.1 API
8.1-1 IsHashSet
8.1-2 HashSet
8.1-3 AddSet
`8.1-4 \in`
8.1-5 RemoveSet
8.1-6 Size
8.1-7 IsEmpty
8.1-8 Set
8.1-9 AsSet
8.1-10 Iterator

### 8 Hashsets

A hash set stores objects and allows efficient lookup whether an object is already a member of the set.

datastructures currently provides a reference implementation of hashsets using a hashtable stored in a plain GAP list.

#### 8.1 API

##### 8.1-1 IsHashSet

`‣ IsHashSet`( arg ) | ( filter )

Returns: `true` or `false`

Category of hashsets

##### 8.1-2 HashSet

`‣ HashSet`( [values][,] [hashfunc[, eqfunc]][,] [capacity] ) | ( function )

Create a new hashset. The optional argument values must be a list of values, which will be inserted into the new hashset in order. The optional argument hashfunc must be a hash- function, eqfunc must be a binary equality testing function that returns `true` if the two arguments are considered equal, and `false` if they are not. Refer to Chapter 6 about the requirements for hashfunctions and equality testers. The optional argument capacity determines the initial size of the hashmap.

##### 8.1-3 AddSet

`‣ AddSet`( hashset, obj ) | ( operation )

Add obj to hashset.

##### `8.1-4 \in`

`‣ \in`( obj, hashset ) | ( operation )

Test membership of obj in hashset

##### 8.1-5 RemoveSet

`‣ RemoveSet`( hashset, obj ) | ( operation )

Remove obj from hashset.

##### 8.1-6 Size

`‣ Size`( hashset ) | ( operation )

Return the size of a hashset Returns an integer

##### 8.1-7 IsEmpty

`‣ IsEmpty`( hashset ) | ( operation )

Returns: a boolean

Test a hashset for emptiness.

##### 8.1-8 Set

`‣ Set`( hashset ) | ( operation )

Returns: a set

Convert a hashset into a GAP set

##### 8.1-9 AsSet

`‣ AsSet`( hashset ) | ( operation )

Returns: an immutable set

Convert a hashset into a GAP set

##### 8.1-10 Iterator

`‣ Iterator`( set ) | ( operation )

Returns: an iterator

Create an iterator for the values contained in a hashset. Note that elements added to the hashset after the creation of an iterator are not guaranteed to be returned by that iterator.

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