NEW: Nominations are now open for the 2019 Swift Community Awards! >>

How to count matching items in an array

Swift version: 5.1

Paul Hudson    @twostraws   

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 }.count

Because 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 }

SAVE 20% ON iOS CONF SG The largest iOS conference in Southeast Asia is back in Singapore for the 5th time in January 2020, now with two days of workshops plus two days of talks on SwiftUI, Combine, GraphQL, and more! Save a massive 20% on your tickets by clicking on this link.

Available from iOS 8.0

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.

MASTER SWIFT NOW
Buy Testing Swift Buy Practical iOS 12 Buy Pro Swift Buy Swift Design Patterns Buy Swift Coding Challenges Buy Server-Side Swift (Vapor Edition) Buy Server-Side Swift (Kitura Edition) Buy Hacking with macOS Buy Advanced iOS Volume One Buy Advanced iOS Volume Two Buy Hacking with watchOS Buy Hacking with tvOS Buy Hacking with Swift Buy Dive Into SpriteKit Buy Swift in Sixty Seconds Buy Objective-C for Swift Developers Buy Beyond Code

Was this page useful? Let us know!

Average rating: 5.0/5