How to Slice an Array in Ruby: Syntax and Examples

In Ruby, you can slice an array using array[start, length] or array[range]. The start is the index where slicing begins, and length is how many elements to take. Using a range like array[1..3] slices from index 1 to 3 inclusive.

Syntax

You can slice an array in Ruby using two main ways:

• array[start, length]: Extracts length elements starting from index start.
• array[range]: Extracts elements within the given range of indices.

Indices start at 0. Negative indices count from the end (-1 is last element).

ruby

array = [10, 20, 30, 40, 50]
slice1 = array[1, 3]   # From index 1, take 3 elements
slice2 = array[2..4]   # From index 2 to 4 inclusive

Example

This example shows how to slice an array using both start, length and range syntax.

ruby

array = ['a', 'b', 'c', 'd', 'e']
slice1 = array[1, 3]
slice2 = array[2..4]
puts "Slice with start,length: #{slice1.inspect}"
puts "Slice with range: #{slice2.inspect}"

Output

Slice with start,length: ["b", "c", "d"]
Slice with range: ["c", "d", "e"]

Common Pitfalls

Common mistakes when slicing arrays in Ruby include:

• Using a negative length, which returns nil.
• Confusing array[start, length] with array[start..end] ranges.
• Expecting slicing to modify the original array (it returns a new array).

ruby

array = [1, 2, 3, 4, 5]
wrong_slice = array[1, -2]  # Returns nil
correct_slice = array[1..-2] # Returns elements from index 1 to second last
puts wrong_slice.inspect
puts correct_slice.inspect

Output

nil
[2, 3, 4]

Quick Reference

Syntax	Description	Example
array[start, length]	Slice from index start, length elements	array[2, 3] => elements at 2,3,4
array[range]	Slice elements within index range	array[1..3] => elements at 1,2,3
array[start..-1]	Slice from start to end	array[2..-1] => from index 2 to last
array[-3, 2]	Slice using negative start index	array[-3, 2] => 3rd last and next element

Key Takeaways

Use array[start, length] to slice a specific number of elements from a start index.

Use array[range] to slice elements between two indices inclusive.

Negative indices count from the end of the array.

Slicing returns a new array and does not change the original.

Avoid negative length values; they return nil.