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Hash

The class for associative arrays or hash tables. The hash table can contain the association from any kind of object to any kind of object. The hash table allocation can be done by the hash expression:

{a=>b,...}

The hash value for the key value is calculated using method Kernel#hash. Since the hash value of the key should not be changed, instances of the classes like Array, Hash, etc. are not suited for the key. When the string used as the key, hash table copies and freeze it and use copied string as the key string. Attempt to Modify the freezed key strings raises an exception.

SuperClass:

Object
Included Modules:

Enumerable
Class Methods:

Hash[key, value...]

Creates a new hash table, interpreting arguments as key - value pair. The number of arguments must be times of two.

new([size])

Creates a new, empty hash table. If size is specified internal space for about size items will be allocated first.

Methods:

self [key]

Returns the value associated to the key. Returns nil, if key is not registered in the hash table.

self [key]= value

Adds binding of key to value. If the value is nil, the binding from key will be removed. That means the hash table cannot holds the association to nil.

clear

Makes the hash table empty.

delete(key)

Deletes the association from key. Returns nil if key is not found in the hash table.

If the block supplied, it will be evaluated when no association matches to key.

delete_if {|key, value|...}

Deletes association from hash table, if the evaluated value of the iterator block with the array of [key,value] as an argument.

each {|key, value|...}
each_pair {|key, value|...}

The iterator which gives each pair of keys and values ([key,value]) to the iterator block.

each_key {|key|...}

Iterates over each key in the hash table.

each_value {|value|...}

Iterates over each value in the hash table.

empty?

Returns true, if hash table is empty.

has_key?(key)
key?(key)
include?(key)

Returns true if hash table has key in the associations.

has_value?(value)
value?(value)

Returns true if hash table has value in the associations.

indexes(ary)
indexes(key_1,..., key_n)

Returns an array of values which keys are specified by arguments.

keys

Returns an array of keys in the hash table.

length
size

Returns the number of associations in the hash table.

invert

Returns the value-to-key mapping of the associative array.

shift

Removes and returns an association from the hash table. The association is in the form [key,value].

to_a

Returns an array of two element arrays of associations which is [key,value].

values

Returns an array of the values in the hash table.


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matz@caelum.co.jp