How to Use map in Ruby: Simple Guide with Examples

In Ruby, map is a method used on arrays to create a new array by applying a block of code to each element. It returns a new array with the transformed values without changing the original array.

Syntax

The map method is called on an array and takes a block that defines how each element should be transformed. The block is enclosed in { } or do...end. The method returns a new array with the results.

• array.map { |element| expression }
• array.map do |element| expression end

ruby

array.map { |element| element * 2 }

Example

This example shows how to double each number in an array using map. The original array stays the same, and a new array with doubled values is created.

ruby

numbers = [1, 2, 3, 4, 5]
doubled = numbers.map { |num| num * 2 }
puts doubled.inspect
puts numbers.inspect

Output

[2, 4, 6, 8, 10]
[1, 2, 3, 4, 5]

Common Pitfalls

One common mistake is expecting map to change the original array. It does not modify the original array but returns a new one. To change the original array, use map!. Another pitfall is forgetting to use a block, which will cause an error.

ruby

arr = [1, 2, 3]
# Wrong: expecting original array to change
arr.map { |x| x + 1 }
puts arr.inspect  # Output: [1, 2, 3]

# Right: use map! to modify original array
arr.map! { |x| x + 1 }
puts arr.inspect  # Output: [2, 3, 4]

Output

[1, 2, 3]
[2, 3, 4]

Quick Reference

Method	Description
map	Returns a new array with the block applied to each element
map!	Modifies the original array by applying the block to each element
map.with_index	Gives the element and its index to the block

Key Takeaways

Use map to create a new array by transforming each element with a block.

map does not change the original array; use map! to modify it.

Always provide a block to map to specify how to transform elements.

The block variable represents each element in the array during iteration.

You can use map.with_index to access element indexes during transformation.