Marcin Doliwa

How to delete elements from an array in Ruby?

In this article I’d like you show you different ways of removing elements from an array in Ruby.

We can remove elements from an array in two fundamental ways, by index and by value.

Removing elements by index

To remove first element, you can use .shift method, to remove the last one, you can .pop it.

> array = [1,2,3,4,5]
 => [1, 2, 3, 4, 5] 
> array.shift
 => 1 
> array
 => [2, 3, 4, 5] 
> array.pop
 => 5 
> array
 => [2, 3, 4] 

To remove element with index N, you can use .delete_at method.

> array = [1,2,3,4,5]
 => [1, 2, 3, 4, 5] 
> n = 1
 => 1
> array.delete_at(n)
 => 2 
> array
 => [1, 3, 4, 5] 

You can also do this by combining an array from two slices, one from index 0 and length N, the second from index N+1 to the last element of an array

> array = [1,2,3,4,5]
 => [1, 2, 3, 4, 5] 
> n = 2
 => 2
> array[0,n] + array[(n+1)..-1]

You can also use .reject/.select with .with_index

> array = [1,2,3,4,5]
 => [1, 2, 3, 4, 5] 
> n = 3
 => 3 
> array.reject.with_index { |_, index| index == n }
 => [1, 2, 3, 5] 

Removing elements by value

If you want to remove all elements of certain value, use .delete method.

> array = [1,2,3,1,2,3]
 => [1, 2, 3, 1, 2, 3] 
> array.delete(1)
 => 1 
> array
 => [2, 3, 2, 3] 
> 

You can also substract an array from an array, it will remove all occurences of elements in the second array

> array = [1,2,3,1,2,3]
 => [1, 2, 3, 1, 2, 3] 
> array - [1,2]
 => [3, 3] 

and of course you can always use .reject/.select methods

> array = [1,2,3,1,2,3]
 => [1, 2, 3, 1, 2, 3] 
> array.reject { |element| element == 1 }
 => [2, 3, 2, 3] 

To delete elements when some condition is met, try .delete_if

> array = [1,2,3,4,5]    
 => [1, 2, 3, 4, 5] 
> array.delete_if(&:odd?)
 => [2, 4] 
> array
 => [2, 4] 

or keep_if if that’s more readable

> array = [1,2,3,4,5]    
 => [1, 2, 3, 4, 5] 
> array.keep_if(&:even?) 
 => [2, 4] 
> array
 => [2, 4] 

It’s important to take notice that some of these methods are changing the original array, the others are returning a new array. I recommend to check documentation of Array class https://ruby-doc.org/core-3.0.3/Array.html

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