哈希键 - 值对的集合，类似这样："employee" => "salary"。它类似于数组，除了索引是通过任意键的任何对象的类型，而不是一个整数索引。

顺序遍历一个哈希键或值要么可能看起来是任意的，一般不会在插入顺序。如果访问的键的哈希值不存在，该方法将返回nil。

创建哈希:

使用数组中，有各种各样的方法来创建哈希值。可以 new 类方法创建一个空的hash ：

months = Hash.new

还可以使用 new 创建哈希，这是一个默认值，否则只是 nil:

months = Hash.new( "month" )

or

months = Hash.new "month"

当访问任何在哈希键，有一个默认值，如果键或值不存在，访问哈希表将返回默认值：

#!/usr/bin/ruby

months = Hash.new( "month" )

puts "#{months[0]}"
puts "#{months[72]}"

这将产生以下结果：

month
month

#!/usr/bin/ruby

H = Hash["a" => 100, "b" => 200]

puts "#{H['a']}"
puts "#{H['b']}"

这将产生以下结果：

100
200

可以使用任何Ruby对象作为键或值，甚至数组，那么下面的例子是一个有效的

[1,"jan"] => "January"

哈希内置的方法：

我们需要有一个Hash对象实例调用哈希方法。正如我们所看到的，下面是Hash对象的方式来创建一个实例：

Hash[[key =>|, value]* ] or

Hash.new [or] Hash.new(obj) [or]

Hash.new { |hash, key| block }

这将返回一个新的哈希值具有给定的对象填充。现在使用创建的对象，我们可以调用任何可用实例方法。例如：

#!/usr/bin/ruby

$, = ", "
months = Hash.new( "month" )

months = {"1" => "January", "2" => "February"}

keys = months.keys

puts "#{keys}"

这将产生以下结果：

2, 1

以下是公共的哈希方法（假设哈希数组对象）：

SN	方法及描述
1	hash == other_hash Tests whether two hashes are equal, based on whether they have the same number of key-value pairs, and whether the key-value pairs match the corresponding pair in each hash.
2	hash.[key] Using a key, references a value from hash. If the key is not found, returns a default value.
3	hash.[key]=value Associates the value given by value with the key given by key.
4	hash.clear Removes all key-value pairs from hash.
5	hash.default(key = nil) Returns the default value for hash, nil if not set by default=. ([] returns a default value if the key does not exist in hash.)
6	hash.default = obj Sets a default value for hash.
7	hash.default_proc Returns a block if hash was created by a block.
8	hash.delete(key) [or] array.delete(key) { |key| block } Deletes a key-value pair from hash by key. If block is used, returns the result of a block if pair is not found. Compare delete_if.
9	hash.delete_if { |key,value| block } Deletes a key-value pair from hash for every pair the block evaluates to true.
10	hash.each { |key,value| block } Iterates over hash, calling the block once for each key, passing the key-value as a two-element array.
11	hash.each_key { |key| block } Iterates over hash, calling the block once for each key, passing key as a parameter.
12	hash.each_key { |key_value_array| block } Iterates over hash, calling the block once for each key, passing the key and value as parameters.
13	hash.each_key { |value| block } Iterates over hash, calling the block once for each key, passing value as a parameter.
14	hash.empty? Tests whether hash is empty (contains no key-value pairs), returning true or false.
15	hash.fetch(key [, default] ) [or] hash.fetch(key) { | key | block } Returns a value from hash for the given key. If the key can't be found, and there are no other arguments, it raises an IndexError exception; if default is given, it is returned; if the optional block is specified, its result is returned.
16	hash.has_key?(key) [or] hash.include?(key) [or] hash.key?(key) [or] hash.member?(key) Tests whether a given key is present in hash, returning true or false.
17	hash.has_value?(value) Tests whether hash contains the given value.
18	hash.index(value) Returns the key for the given value in hash, nil if no matching value is found.
19	hash.indexes(keys) Returns a new array consisting of values for the given key(s). Will insert the default value for keys that are not found. This method is deprecated. Use select.
20	hash.indices(keys) Returns a new array consisting of values for the given key(s). Will insert the default value for keys that are not found. This method is deprecated. Use select.
21	hash.inspect Returns a pretty print string version of hash.
22	hash.invert Creates a new hash, inverting keys and values from hash; that is, in the new hash, the keys from hash become values, and values become keys.
23	hash.keys Creates a new array with keys from hash.
24	hash.length Returns the size or length of hash as an integer.
25	hash.merge(other_hash) [or] hash.merge(other_hash) { |key, oldval, newval| block } Returns a new hash containing the contents of hash and other_hash, overwriting pairs in hash with duplicate keys with those from other_hash.
26	hash.merge!(other_hash) [or] hash.merge!(other_hash) { |key, oldval, newval| block } Same as merge, but changes are done in place.
27	hash.rehash Rebuilds hash based on the current values for each key. If values have changed since they were inserted, this method reindexes hash.
28	hash.reject { |key, value| block } Creates a new hash for every pair the block evaluates to true
29	hash.reject! { |key, value| block } Same as reject, but changes are made in place.
30	hash.replace(other_hash) Replaces the contents of hash with the contents of other_ hash.
31	hash.select { |key, value| block } Returns a new array consisting of key-value pairs from hash for which the blockreturns true.
32	hash.shift Removes a key-value pair from hash, returning it as a two-element array.
33	hash.size Returns the size or length of hash as an integer.
34	hash.sort Converts hash to a two-dimensional array containing arrays of key-value pairs, then sorts it as an array.
35	hash.store(key, value) Stores a key-value pair in hash.
36	hash.to_a Creates a two-dimensional array from hash. Each key/value pair is converted to an array, and all these arrays are stored in a containing array.
37	hash.to_hash Returns hash (self).
38	hash.to_s Converts hash to an array, then converts that array to a string.
39	hash.update(other_hash) [or] hash.update(other_hash) {|key, oldval, newval| block} Returns a new hash containing the contents of hash and other_hash, overwriting pairs in hash with duplicate keys with those from other_hash.
40	hash.value?(value) Tests whether hash contains the given value.
41	hash.values Returns a new array containing all the values of hash.
42	hash.values_at(obj, ...) Returns a new array containing the values from hash that are associated with the given key or keys.