BLACK FRIDAY: Save 50% on all books and bundles! >>

How to transform a dictionary using mapValues()

Swift version: 5.2

Paul Hudson    @twostraws   

Although dictionaries have a general map() method, they also have a specialized form of map() called mapValues() – it transforms just the values of the dictionary, leaving the keys untouched.

This extra method is useful because dictionaries can’t have duplicate keys, but if you’re only transforming the values from a dictionary then this is not a problem.

Let’s try it out on a dictionary containing the height in centimeters of various people:

let peopleMetric = ["Taylor": 178.0, "Justin": 175.0, "Ed": 173.0]

If we want to convert those heights to inches without changing the keys, we can use mapValues() like this:

let peopleImperial = peopleMetric.mapValues { $0 / 2.54 }

Save 50% in my Black Friday sale.

Sponsor Hacking with Swift and reach the world's largest Swift community!

Available from iOS 8.0 – learn more in my book Pro Swift

Similar solutions…

About the Swift Knowledge Base

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

BUY OUR BOOKS
Buy Pro Swift Buy Swift Design Patterns Buy Testing Swift Buy Hacking with iOS Buy Swift Coding Challenges Buy Swift on Sundays Volume One Buy Server-Side Swift (Vapor Edition) Buy Advanced iOS Volume One Buy Advanced iOS Volume Two Buy Advanced iOS Volume Three Buy Hacking with watchOS Buy Hacking with tvOS Buy Hacking with macOS Buy Dive Into SpriteKit Buy Swift in Sixty Seconds Buy Objective-C for Swift Developers Buy Server-Side Swift (Kitura Edition) Buy Beyond Code

Was this page useful? Let us know!

Average rating: 5.0/5

Link copied to your pasteboard.