Removing duplicates in swift, keeping order

remove_duplicates.swift

var arr = [1, 1, 1, 2, 2, 3, 4, 5, 6, 6, 6, 6, 6, 7, 8]
var list = ["A","A","A","A","A","A","B","C","D","E","E","E","E"]

let set = Set(arr) // no duplicates but no order either
let orderedSet = NSOrderedSet(array: arr) // no duplicates and ordered, but not an array
let arrayFromOrderedSet = Array(NSOrderedSet(array: arr)) // is array, ordered, no duplicates, but loses type info
let sorted = Array(Set(arr)).sorted() // is array, ordered, no duplicates, keeps type info, but limited to ascending order

extension Array where Element: Equatable {

    func duplicatesRemoved() -> [Element] {
        return reduce([]) { $0.contains($1) ? $0 : $0 + [$1] }
    }

    mutating func removeDuplicates() {
        self = duplicatesRemoved()
    }
}

list.duplicatesRemoved() // new list -> ["A", "B", "C", "D", "E"]
list.removeDuplicates() // same list -> ["A", "B", "C", "D", "E"]

arr.duplicatesRemoved() // new list -> [1, 2, 3, 4, 5, 6, 7, 8]
arr.removeDuplicates() // same list -> [1, 2, 3, 4, 5, 6, 7, 8]

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