How to remove duplicate items from an array
Swift version: 5.4
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()
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Available from iOS 8.0
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