NEW: Master Swift design patterns with my latest book! >>

How to filter a loop using a where clause

Written by Paul Hudson    @twostraws

A regular for-in loop goes over all the items in an array, allowing you to manipulate them as you need. However, sometimes you don’t need all items and instead only want a subset, and in those circumstances the where keyword is useful.

For example, consider this array:

let names = ["Michael Jackson", "Taylor Swift", "Michael Caine", "Adele Adkins", "Michael Jordan"]

A regular for-in loop could print out all those names, but by adding a where clause we could restrict the loop so it operates only on people named Michael:

for name in names where name.hasPrefix("Michael") {
    print(name)
}

If you need multiple conditions in your where clause, join them using &&.

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

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

Other people are reading…

About the Swift Knowledge Base

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

Upgrade to premium

The Hacking with Swift guide book helps you learn faster, plus get an Xcode tips and tricks video and Swift wall chart.

Click here to visit the Hacking with Swift store >>