NEW: Join my free 100 Days of SwiftUI challenge today! >>

How to find the difference between two arrays

Swift version: 5.1

Paul Hudson    @twostraws   

If you have two arrays that contain similar items and want to find out their differences – i.e., which items exist in one or the other, but not both – the easiest thing to do is use a Set. Sets have a symmetricDifference() method that does exactly this, so you just need to convert both arrays to a set, then convert the result back into an array.

Here’s an extension to make it easier:

extension Array where Element: Hashable {
    func difference(from other: [Element]) -> [Element] {
        let thisSet = Set(self)
        let otherSet = Set(other)
        return Array(thisSet.symmetricDifference(otherSet))
    }
}

And here’s some example code you can use to try it out:

let names1 = ["John", "Paul", "Ringo"]
let names2 = ["Ringo", "Paul", "George"]
let difference = names1.difference(from: names2)

That will set difference to be ["George", "John"], because those are the two names that only appear once in either array.

LEARN SWIFTUI FOR FREE I have a massive, free SwiftUI video collection on YouTube teaching you how to build complete apps with SwiftUI – check it out!

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.

BUY OUR BOOKS
Buy Pro Swift Buy Swift Design Patterns Buy Testing Swift Buy Hacking with iOS Buy Swift Coding Challenges Buy Swift on Sundays Volume One Buy Server-Side Swift (Vapor Edition) Buy Advanced iOS Volume One Buy Advanced iOS Volume Two Buy Advanced iOS Volume Three Buy Hacking with watchOS Buy Hacking with tvOS Buy Hacking with macOS Buy Dive Into SpriteKit Buy Swift in Sixty Seconds Buy Objective-C for Swift Developers Buy Server-Side Swift (Kitura Edition) Buy Beyond Code

Was this page useful? Let us know!

Average rating: 4.8/5