How to count matching items in an array
Swift version: 5.2
If you want to count how many items in an array (or any collection) match a test you specify, the easiest thing to do is run the collection through a call to filter() then count the remainder.
For example, if you had an array of numbers and wanted to count how many were odd, you would write this:
let count1 = [1, 2, 3, 4, 5].filter { $0 % 2 == 1 }.countBecause this is something that all collections might want to do, you should consider wrapping it in an extension on Collection, like this:
extension Collection {
func count(where test: (Element) throws -> Bool) rethrows -> Int {
return try self.filter(test).count
}
}With that change, counting the odd numbers becomes this:
let count2 = [1, 2, 3, 4, 5].count { $0 % 2 == 1 }
SPONSORED Announcing NSSpain 2020: Remote Edition! An online, continuous conference for iOS developers. We’ll start on Thursday and finish on Friday, with talks, activities, and lots of fun for 36 hours, non-stop. Sound good? Join us!
Sponsor Hacking with Swift and reach the world's largest Swift community!
Available from iOS 8.0
Similar solutions…
- How do you create multi-dimensional arrays?
- How to add drag and drop to your app
- What is a monad?
- How to convert a multidimensional array to a single-dimensional array
- How to count element frequencies in an array
About the Swift Knowledge Base
This is part of the Swift Knowledge Base, a free, searchable collection of solutions for common iOS questions.
