Swift version: 5.2
One of Swift’s lesser-known functions is prefix(while:)
: call this on an array along with a test to apply, and it will return as many items from the start of the array as it can, stopping only when it reaches the first element that fails your test.
For example, if we had an array of test scores:
let scores = [89, 86, 96, 78, 92, 100]
We could use prefix(while:)
to return all scores over 85 that occurred before the first score below 85 – i.e., find me all the passing scores that took place before the first person failed.
Here’s that in Swift:
let initialPasses1 = scores.prefix { $0 > 85 }
You can apply any test you want, and sometimes you’ll get back an empty array if the very first element fails your test. For example, this will return an empty array:
let initialPasses2 = scores.prefix { $0 < 85 }
SPONSORED Would you describe yourself as knowledgeable, but struggling when you have to come up with your own code? Fernando Olivares has a new book containing iOS rules you can immediately apply to your coding habits to see dramatic improvements, while also teaching applied programming fundamentals seen in refactored code from published apps.
Sponsor Hacking with Swift and reach the world's largest Swift community!
Available from iOS 8.0
This is part of the Swift Knowledge Base, a free, searchable collection of solutions for common iOS questions.
Link copied to your pasteboard.