Ruby in a Nutshell

Name

Hash — Hash class

Synopsis

Hash is a class for collection of key-value pairs, or in other words, a collection indexed by arbitrary type of objects, which define proper hash and eql? methods.

Included Module

Enumerable

Class Methods

Hash[key, value...]

Creates a Hash.

Hash[1,2,2,4]  # => {1=>2, 2=>4}

Hash::new([default=nil])

Creates a Hash. A default value may also be specified.

h = Hash::new(15)   # => {}
h[44]               # => 15 (no key; default returned)

Instance Methods

Methods of the Hash class ending in a pipe ! modify their receiver and return a hash if modification took place, otherwise nil. Methods without a ! return a modified copy of the hash.

h[key]

Returns the value associated with key.

h[key]=value

Associates value with key.

h.clear

Deletes all key-value pairs from h.

h = {1=>2, 2=>4}
h.clear
h                  # => {}
h = {1=>2, 2=>4}
h.delete_if{|k,v| k % 2 == 0}
h         # => {1=>2}

h.default

Returns the default value for a key that doesn’t exist. Note that the default value isn’t copied, so that modifying the default object may affect all default values thereafter.

h.default=value

Sets the default value.

h.delete(key)

Deletes a key-value pair with a key equal to key.

h.delete_if {|key, value|...}

Deletes key-value pairs where the evaluated result of block is true.

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

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

Executes the block once for each key-value pair. Pairs are in unspecified order.

h.each_key {|key|...}

Executes the block once for each key. Keys are in unspecified order.

h.each_value {|value|...}

Executes ...