# HackerRank Ruby Array Selection Solution

Hello coders, In this post, you will learn how to solve HackerRank Ruby Array Selection Solution. This problem is a part of the Ruby Tutorial series. One more thing to add, don’t straight away look for the solutions, first try to solve the problems by yourself. If you find any difficulty after trying several times, then look for the solutions.

## HackerRank Ruby Array Selection Solution

Let’s get started with Ruby Array Selection Solution

### Problem Statement

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.

### HackerRank Ruby Array Selection Solution

```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 Chase2Learn. This tutorial is only for Educational and Learning purpose.

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