BLACK FRIDAY: Save 50% on all our Swift books and bundles! >>

How to remove duplicate items from an array

Swift version: 5.4

Paul Hudson    @twostraws   

There are several ways of removing duplicate items from an array, but one of the easiest is with the following extension on Array:

extension Array where Element: Hashable {
    func removingDuplicates() -> [Element] {
        var addedDict = [Element: Bool]()

        return filter {
            addedDict.updateValue(true, forKey: $0) == nil
        }
    }

    mutating func removeDuplicates() {
        self = self.removingDuplicates()
    }
}

That provides two methods: one called removingDuplicates() that returns an array with duplicates removed, and one called removeDuplicates() that changes the array in place.

The method works using filter() and a dictionary: when you call updateValue() on a dictionary it returns nil if the key is new, so we can use that to figure out which items are unique.

For example:

let numbers = [1, 5, 3, 4, 5, 1, 3]
let unique = numbers.removingDuplicates()
Save 50% in my Black Friday sale.

SAVE 50% This Black Friday all our books and bundles are half price, so you can take your Swift knowledge further without spending big! Get the Swift Power Pack to build your iOS career faster, get the Swift Platform Pack to builds apps for macOS, watchOS, and beyond, or get the Swift Plus Pack to learn advanced design patterns, testing skills, and more.

Save 50% on all our books and bundles!

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: 4.6/5

 
Unknown user

You are not logged in

Log in or create account
 

Link copied to your pasteboard.