How to use map() to transform an array

Swift version: 5.0

Paul Hudson    @twostraws    March 28th 2019

The map() method allows us to transform arrays (and indeed any kind of collection) using a transformation closure we specify. The return value will be an array of the same size, containing your transformed elements.

For example, given the following array:

let numbers = [1, 2, 3, 4]

We could use map() to transform those numbers so they are doubled, like this:

let doubled = numbers.map { $0 * 2 }

You can map whatever you want. For example, you could convert an array of strings to be uppercase:

let strings = ["John", "Paul", "George", "Ringo"]
let uppercased = strings.map { $0.uppercased() }

Available from iOS – learn more in my book Pro Swift

Did this solution work for you? Please pass it on!

Tweet

Other people are reading…

• What are static methods and variables?
• What are implicitly unwrapped optionals?
• What is key-value observing?
• What’s the difference between Any and AnyObject?
• How to run code when an object is destroyed

About the Swift Knowledge Base

This is part of the Swift Knowledge Base, a free, searchable collection of solutions for common iOS questions.