How to Map an Array in Ruby: Simple Guide with Examples

In Ruby, you can use the map method to transform each element of an array into a new array. It takes a block where you define how to change each item, returning a new array with the results.

Syntax

The map method is called on an array and takes a block that specifies how to transform each element. The syntax is:

array.map { |element| transformation }

Here, element is each item in the array, and transformation is the code that changes it.

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]
doubled = numbers.map { |n| n * 2 }
puts doubled.inspect

Output

[2, 4, 6, 8]

Common Pitfalls

A common mistake is using map without a block or forgetting to return the transformed value inside the block. Also, map returns a new array and does not change the original array unless you use map!.

Wrong example (no block):

numbers.map

Right example:

numbers.map { |n| n + 1 }

ruby

numbers = [1, 2, 3]
# Wrong: no block given
# numbers.map # This will raise an error

# Right:
numbers.map { |n| n + 1 }

Quick Reference

Method	Description
map	Returns a new array with the block's results for each element
map!	Modifies the original array with the block's results
each	Iterates over elements but returns the original array unchanged

Key Takeaways

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

map does not change the original array unless you use map!.

Always provide a block that returns the transformed value for each element.

If you don't need a new array, use each instead of map.