Ruby Array.rrindex() Method

By IncludeHelp Last updated : November 29, 2024

In this article, we will study about Array.rindex() method. You all must be thinking the method must be doing something which is related to finding the index of certain elements. It is not as simple as it looks. Well, we will figure this out in the rest of our content. We will try to understand it with the help of syntax and demonstrating program codes.

Description and Usage

This method is a public instance method and defined for the Array class in Ruby's library. This method works in such a way that it returns the index of the object which is passed as an argument in the method but with a twist, it checks from the end of the Array instance. For instance, if there are three "s" in the Array object then it will return the index of the last "s". If a block is provided instead of an argument then it returns the index of the first object for which the block stands to be true starting from the last or end of the Array. This method will return "nil" if no match is found.

Syntax

array_instance.rindex(object) -> int, nil
or
array_instance.rindex{|item| block} -> int, nil

Parameters

If this method is not invoked with the block, this method takes one argument which is the name of the object for which the search is going to be held.

Example 1

=begin
  Ruby program to demonstrate rindex method
=end

# array declaration
lang = ["C++","Java","Java","Java","Python","Html","Javascript","php","Ruby","Kotlin"]

puts "Enter the element you want to search"
ele = gets.chomp

if (lang.rindex(ele))
  puts "#{ele} found at #{lang.rindex(ele)} index"
else
	puts "#{ele} does not exist"
end

Output

Enter the element you want to search 
Java
Java found at 3 index

Explanation

In the above code, you can observe that we are finding the index of the object with the help of the Array.rindex() method. The object "Java" is present at three different indexes namely 1, 2 and 3 but the method is returning index 3 because in the case of the rindex() method, the search starts from the end of the Array instance.

Example 2:

=begin
  Ruby program to demonstrate rindex method
=end

# array declaration
lang = ["C++","Java","Java","Java","Python","Html","Javascript","php","Ruby","Kotlin"]

puts "Enter the element you want to search"
ele = gets.chomp

if (lang.rindex{|item| item == ele})
  puts "#{ele} found at #{lang.rindex{|item| item == ele}} index"
else
	puts "#{ele} does not exist"
end

Output

Enter the element you want to search 
Java
Java found at 3 index

Explanation

In the above code you can observe that instead of argument, we are invoking the method with a block. The object "Java" is present at three different indexes namely 1, 2 and 3 but the method is returning index 3 because in the case of rindex() method, the search starts from the end of the Array instance.

Ruby Array.index() Method

Ruby Array.each_index Method

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