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Hash.compact Method with Example in Ruby

Ruby Hash.compact Method: Here, we are going to learn about the Hash.compact Method with examples in Ruby programming language.
Submitted by Hrithik Chandra Prasad, on February 16, 2020

Hash.compact Method

In this article, we will study about Hash.compact Method. The working of this method can be predicted with the help of its name but it is not as simple as it seems. Well, we will understand this method with the help of its syntax and program code in the rest of the content.

Method description:

This method is a public instance method that is defined in Ruby's library especially for the Hash class. This method is one of the examples of non-destructive methods where the changes brought by the method are not permanent or temporary. These types of methods do not affect the self Hash instance. This method works in a way that removes all the keys from the hash which are containing nil values and returns a new Hash object which does not contain any nil value.

Syntax:

    Hash_object.compact

Argument(s) required:

This method does not take any argument.

Example 1:

=begin
  Ruby program to demonstrate compact method
=end	

hash1= {"color"=> "Black", "object"=>nil, "love"=>"mom","fruit"=>"Kiwi","vege"=>"potato"}

puts "Hash compact implementation"

puts "Elements after compact operation: #{hash1.compact}"
puts "Array elements are:"
puts "#{hash1}"

Output

Hash compact implementation
Elements after compact operation: {"color"=>"Black", "love"=>"mom", "fruit"=>"Kiwi", "vege"=>"potato"}
Array elements are:
{"color"=>"Black", "object"=>nil, "love"=>"mom", "fruit"=>"Kiwi", "vege"=>"potato"}

Explanation:

In the above code, you can observe that we are removing nil value keys from the hash object with the help of the Hash.compact method. This method is not bringing any changes in the actual hash instance because this method is an example of the non-destructive method and you can observe this by yourself when the program is printing the original hash on which the method has been invoked.

Example 2:

=begin
  Ruby program to demonstrate compact method
=end	

hash1= {"color"=> [nil,nil,"black"], "object"=>nil, "love"=>"mom","fruit"=>"Kiwi","vege"=>"potato"}

puts "Hash compact implementation"

puts "Elements after compact operation: #{hash1.compact}"
puts "Array elements are:"
puts "#{hash1}"

Output

Hash compact implementation
Elements after compact operation: {"color"=>[nil, nil, "black"], "love"=>"mom", "fruit"=>"Kiwi", "vege"=>"potato"}
Array elements are:
{"color"=>[nil, nil, "black"], "object"=>nil, "love"=>"mom", "fruit"=>"Kiwi", "vege"=>"potato"}

Explanation:

In the above code, you can observe that the Hash.compact method does not work upon the hashes which have keys along with more than one value. The method is returning the original hash without removing the nil value keys.