Ruby Array – Selection Solution

In this post, we will solve Ruby Array – Selection HackerRank Solution. This problem (Ruby Array – Selection) is a part of HackerRank Ruby series.

Task

The array class also allows to select and return a subset of an array based on some criteria defined in a block (a block is a group of code within {} that accepts a variable and returns a value).

• Selecting elements that satisfy a given criteria
• Rejecting elements that satisfy a given criteria

 > arr = [3, 4, 2, 1, 2, 3, 4, 5, 6]
 > arr.select {|a| a > 2}
 => [3, 4, 3, 4, 5, 6]
 > arr.reject {|a| a > 2}
 => [2, 1, 2]
 > arr
 => [3, 4, 2, 1, 2, 3, 4, 5, 6]
 > arr.drop_while {|a| a > 1} # removes elements till the block returns false for the first time
 => [1, 2, 3, 4, 5, 6]

As you can see, the original array remains unchanged. This is called Non-Destructive Selection.
For destructive behavior (change to the original array), Ruby provides the following methods:

 > arr = [3, 4, 2, 1, 2, 3, 4, 5, 6]  
 > arr.delete_if {|a| a < 2}
  => [3, 4, 2, 2, 3, 4, 5, 6]  
 > arr.keep_if {|a| a < 4}  
 => [3, 2, 2, 3]

Note

• An element in a block is selected, rejected, deleted, or kept based on the True or False value generated by that block on that element.
• For a destructive behavior for select and reject or any method that one wants to enforce a change in the original array, a ! can be used at the end of the method i.e., select! and reject!

In this challenge, you have to complete the functions below using syntax as explained above.

Solution – Ruby Array – Selection

def select_arr(arr)
  # select and return all odd numbers from the Array variable `arr`
  arr.select{ |a| (a%2 != 0)}
end

def reject_arr(arr)
  # reject all elements which are divisible by 3
  arr.reject {|a| (a%3 == 0)}
end

def delete_arr(arr)
  # delete all negative elements
  arr.delete_if {|a| a<0}
end

def keep_arr(arr)
  # keep all non negative elements ( >= 0)
  arr.keep_if {|a| a>=0}
end

Note: This problem (Ruby Array – Selection) is generated by HackerRank but the solution is provided by CodingBroz. This tutorial is only for Educational and Learning purpose.