Ruby Hash

Ruby Hash

Create a hash

Like arrays, there are different ways to create hashes. You can create an empty hash by the new class method:

months = Hash.new

You can also use new to create a hash with a default value, and a hash without a default value is nil:

months = Hash.new( "month" )

或

months = Hash.new "month"

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

#!/usr/bin/ruby

months = Hash.new( "month" )

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

This results in the following:

month
month

#!/usr/bin/ruby

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

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

This results in the following:

100
200

You can use any Ruby object as a key or value, or even an array, so the following example is a valid one:

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

Hash built-in methods

We need an instance of the Hash object to call the Hash method. Here's how to create an instance of a Hash object:

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

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

Hash.new { |hash, key| block }

This returns a new hash that is populated with a given object. N ow, with the created object, we can call any available instance method. For example:

#!/usr/bin/ruby

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

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

keys = months.keys

puts "#{keys}"

This results in the following:

2, 1

Here's the common hash method (assuming hash is a Hash object):