NEW: My new book Pro SwiftUI is out now – level up your SwiftUI skills today! >>

Transforming and unwrapping dictionary values with compactMapValues()

Available from Swift 5.0

Paul Hudson      @twostraws

SE-0218 adds a new compactMapValues() method to dictionaries, bringing together the compactMap() functionality from arrays (“transform my values, unwrap the results, then discard anything that’s nil”) with the mapValues() method from dictionaries (“leave my keys intact but transform my values”).

As an example, here’s a dictionary of people in a race, along with the times they took to finish in seconds. One person did not finish, marked as “DNF”:

let times = [
    "Hudson": "38",
    "Clarke": "42",
    "Robinson": "35",
    "Hartis": "DNF"
]

We can use compactMapValues() to create a new dictionary with names and times as an integer, with the one DNF person removed:

let finishers1 = times.compactMapValues { Int($0) }

Alternatively, you could just pass the Int initializer directly to compactMapValues(), like this:

let finishers2 = times.compactMapValues(Int.init)

You can also use compactMapValues() to unwrap optionals and discard nil values without performing any sort of transformation, like this:

let people = [
    "Paul": 38,
    "Sophie": 8,
    "Charlotte": 5,
    "William": nil
]

let knownAges = people.compactMapValues { $0 }
Hacking with Swift is sponsored by Stream

SPONSORED Build Chat messaging quickly with Stream Chat. The Stream iOS Chat SDK is highly flexible, customizable, and crazy optimized for performance. Take advantage of this top-notch developer experience, get started for free today!

Click here

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

Other changes in Swift 5.0…

Download all Swift 5.0 changes as a playground Link to Swift 5.0 changes

Browse changes in all Swift versions

 
Unknown user

You are not logged in

Log in or create account
 

Link copied to your pasteboard.