How to Chunk an Array in Ruby: Simple Guide

In Ruby, you can split an array into smaller arrays (chunks) using the each_slice method from the Enumerable module. For example, array.each_slice(3).to_a divides the array into chunks of 3 elements each.

Syntax

The main method to chunk an array in Ruby is each_slice(n), where n is the size of each chunk. It returns an Enumerator that yields slices of the array with n elements.

You can convert this Enumerator to an array of arrays by calling to_a.

ruby

array.each_slice(n).to_a

Example

This example shows how to split an array of numbers into chunks of 3 elements each using each_slice. The result is an array of smaller arrays.

ruby

array = [1, 2, 3, 4, 5, 6, 7, 8]
chunks = array.each_slice(3).to_a
puts chunks.inspect

Output

[[1, 2, 3], [4, 5, 6], [7, 8]]

Common Pitfalls

A common mistake is to try using chunk method expecting it to split the array into fixed-size parts. However, chunk groups elements by a condition and is not for fixed-size chunks.

Also, forgetting to convert the Enumerator to an array with to_a can cause unexpected results.

ruby

array = [1, 2, 3, 4, 5]
# Wrong: chunk groups by condition, not size
result = array.chunk { |x| x < 3 }.to_a
puts result.inspect

# Right: use each_slice for fixed-size chunks
result = array.each_slice(2).to_a
puts result.inspect

Output

[[true, [1, 2]], [false, [3, 4, 5]]]
[[1, 2], [3, 4], [5]]

Quick Reference

• each_slice(n): Splits array into chunks of size n.
• to_a: Converts Enumerator to array.
• chunk: Groups elements by condition, not size.

Key Takeaways

Use each_slice(n).to_a to split an array into chunks of size n.

The chunk method is for grouping by condition, not fixed-size chunks.

Always convert the Enumerator returned by each_slice to an array with to_a.

Chunks may have fewer elements if the array size isn't divisible by chunk size.

This method works on any Enumerable, including arrays.