How to remove duplicate items from an array
Swift version: 5.2
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()
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?
- What is a monad?
- How to convert a multidimensional array to a single-dimensional array
- How to add drag and drop to your app
- How to remove the first or last item from 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.
