Ruby Hash

Creating a Hash

As with arrays, there are various ways to create a hash. You can create an empty hash via the new class method:

months = Hash.new

You can also create a hash with and without the default value using new The hash is nil:

months = Hash.new( "month" )

或

months = Hash.new "month"

When you access any key in a hash with a default value, accessing the hash will return the default value if the key or value does not exist:

#!/usr/bin/ruby

months = Hash.new( "month" )

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

The output result of the above instance is:

month
month

#!/usr/bin/ruby

H = Hash["a" => 100, "b" => 200]

puts "#{H['a']}"
puts "#{H['b']}"

The output result of the above instance is:

100
200

You can use any Ruby object as a key or value, or even an array, as shown in the following example:

[1,"jan"] => "January"

Hash built-in method

If you need to call the Hash method, you need to first Instantiate a Hash object. Here's how to create a Hash object instance:

Hash[[key =>|, value]* ] or

Hash.new [or] Hash.new(obj) [or]

Hash.new { |hash, key| block }

This will return a new hash populated with the given object. Now, using the created object, we can call any of the available methods. For example:

#!/usr/bin/ruby

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

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

keys = months.keys

puts "#{keys}"

The output result of the above example is:

["1", "2"]

The following is a public hash method (assuming hash is a Hash object):

23242526272829hash.reject! { |key, value| block }30hash.replace(other_hash)

Serial number	Method & Description
1	hash == other_hash Check whether two hashes have the same number of key-value pairs and whether the key-value pairs match each other to determine whether the two hashes are equal.
2	hash.[key] Use a key to reference a value from a hash. If the key is not found, the default value is returned.
3	hash.[key]=value Compare the value given by value with key Association with the given key.
4	hash.clear Remove all key-value pairs from the hash.
5	hash.default(key = nil) Returns the default value of hash, if not If set via default=, nil will be returned. (If the key does not exist in hash, [] returns a default value.)
6	hash.default = obj Sets the default value for hash.
7	hash.default_proc If hash is created via a block, the block is returned.
8	hash.delete(key) [or] array.delete(key) { |key| block } Delete key-value pairs from hash via key. If a block is used and no matching key-value pair is found, the result of the block is returned. Compare this to delete_if.
9	hash.delete_if { |key,value| block } is block for true Each block, remove key-value pairs from hash.
10	hash.each { |key,value| block } Traverse hash, for each Each key calls block once, passing key-value as a two-element array.
11	hash.each_key { |key| block } Traverse hash, for each key Call the block once, passing key as the parameter.
12	hash.each_key { |key_value_array| block } Traverse hash, for each key Call the block once, passing key and value as parameters.
13	hash.each_value { |value| block } Traverse hash, for each key Call the block once, passing value as the parameter.
14	hash.empty? Check whether the hash is empty (does not contain key-value pairs) and returns true or false.
15	hash.fetch(key [, default] ) [or] hash.fetch(key) { | key | block } Returns the value from hash given the given key. If key is not found and no other parameters are supplied, an IndexError exception is thrown; if default is given, default is returned ;If the optional block is specified, the result of the block is returned.
16	hash.has_key?(key) [or] hash.include?(key) [or] hash.key?( key) [or] hash.member?(key) Checks whether the given key exists in the hash, returns true or false.
17	hash.has_value?(value) Checks if the hash contains the given value .
18	hash.index(value) Returns the hash for the given value key, or nil if no matching value is found.
19	hash.indexes(keys) Returns a new array consisting of the values ​​of the given keys. Keys not found will have default values ​​inserted. This method is deprecated, please use select.
20	hash.indices(keys) Returns a new array consisting of the values ​​of the given keys. Keys not found will have default values ​​inserted. This method is deprecated, please use select.
21	hash.inspect Returns the printed string version of the hash.
22	hash.invert Create a new hash, invert hash##keys and values in #. That is, in the new hash, the keys in hash will become values, and the values ​​will become keys.
	hash.keysCreates a new array with the keys in hash. /td>
	hash.lengthReturns the size or length of hash in integer form.
	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, rewriting the keys in the hash with duplicate keys from other_hash value pair.
	hash.merge!(other_hash) [or]hash.merge!(other_hash) { |key, oldval, newval| block } is the same as merge, but in fact the hash has changed.
	hash.rehashRebuild the hash based on the current value of each key . This method will re-index hash if the value has changed since insertion.
	hash.reject { |key, value| block } is block is ## Create a new hash for each key-value pair of #true.
	is the same as reject , But in fact the hash has changed.
	Replace the contents of hash with the contents of other_hash.
31	hash.select { |key, value| block } Returns a new array, consisting of block Returns the key-value pairs in hash of true.
32	hash.shift Remove a key-value pair from hash and shift the Key-value pairs are returned as a two-element array.
33	hash.size Returns the size of hash in integer form or length.
34	hash.sort Convert hash into a two-dimensional array containing key-value pairs array and then sort it.
35	hash.store(key, value) Storage a key-value pair in hash .
36	hash.to_a Create a two-dimensional array from hash. Each key-value pair is converted to an array and all these arrays are stored in an array.
37	hash.to_hash returns hash(self).
38	hash.to_s Convert hash to an array, and then convert the 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, rewriting hash with other_hash Key-value pairs with duplicate keys.
40	hash.value?(value) Check if 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 hash The value associated with the given key.