GAP (datastructures) - Chapter 7: Hashmaps

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7 Hashmaps
7.1 API
7.1-1 IsHashMap
7.1-2 HashMap
7.1-3 Keys
7.1-4 Values
7.1-5 KeyIterator
7.1-6 ValueIterator
7.1-7 KeyValueIterator
`7.1-8 \[\]`
`7.1-9 \[\]\:\=`
`7.1-10 \in`
`7.1-11 IsBound\[\]`
`7.1-12 Unbind\[\]`
7.1-13 Size
7.1-14 IsEmpty

### 7 Hashmaps

A hash map stores key-value pairs and allows efficient lookup of keys by using a hash function.

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

#### 7.1 API

##### 7.1-1 IsHashMap

`‣ IsHashMap`( arg ) | ( filter )

Returns: `true` or `false`

Category of hash maps

##### 7.1-2 HashMap

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

Create a new hash map. The optional argument values must be a list of key-value pairs which will be inserted into the new hashmap 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.

##### 7.1-3 Keys

`‣ Keys`( h ) | ( operation )

Returns: a list

Returns the list of keys of the hashmap h.

##### 7.1-4 Values

`‣ Values`( h ) | ( operation )

Returns: a list

Returns the set of values stored in the hashmap h.

##### 7.1-5 KeyIterator

`‣ KeyIterator`( h ) | ( operation )

Returns: an iterator

Returns an iterator for the keys stored in the hashmap h.

##### 7.1-6 ValueIterator

`‣ ValueIterator`( h ) | ( operation )

Returns: an iterator

Returns an iterator for the values stored in the hashmap h.

##### 7.1-7 KeyValueIterator

`‣ KeyValueIterator`( h ) | ( operation )

Returns: an iterator

Returns an iterator for key-value-pairs stored in the hashmap h.

##### `7.1-8 \[\]`

`‣ \[\]`( hashmap, object ) | ( operation )

List-style access for hashmaps.

##### `7.1-9 \[\]\:\=`

`‣ \[\]\:\=`( hashmap, object, object ) | ( operation )

List-style assignment for hashmaps.

##### `7.1-10 \in`

`‣ \in`( object, hashmap ) | ( operation )

Test whether a key is stored in the hashmap.

##### `7.1-11 IsBound\[\]`

`‣ IsBound\[\]`( object, hashmap ) | ( operation )

Test whether a key is stored in the hashmap.

##### `7.1-12 Unbind\[\]`

`‣ Unbind\[\]`( object, hashmap ) | ( operation )

Delete a key from a hashmap.

##### 7.1-13 Size

`‣ Size`( hashmap ) | ( operation )

Determine the number of keys stored in a hashmap.

##### 7.1-14 IsEmpty

`‣ IsEmpty`( object, hashmap ) | ( operation )

Test whether a hashmap is empty.

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