Ruby Hashes (Hash)

Creating a hash

Like arrays, there are various ways to create hashes. You can create a hash by new Class method to create an empty hash:

months = Hash.new

You can also use new Create a hash with a default value, a hash without a default value is nil:

months = Hash.new("month")
　
or
　
months = Hash.new "month"

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

Online Example

#!/usr/bin/ruby
　
months = Hash.new("month")
　
puts "#{months[0]}"
puts "#{months[72"]"

The output result of the above example is:

month
month

Online Example

#!/usr/bin/ruby
　
H = Hash["a" =>　100, "b" =>　200]
　
puts "#{H['a']}"
puts "#{H['b']}"

The output result of the above example is:

100
200

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

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

Built-in Hash Methods

If you need to call a Hash method, you must first instantiate a Hash object. Below are some ways to create a Hash object:

Hash[[key =>|, value]*　] or
　
Hash.new [or] Hash.new(obj) [or]
　
Hash.new { |hash, key| block }

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

Online 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"]

Below are the public hash methods (assuming hash Is a Hash object):