How to create array of unique object list in Swift

Question

How can we create unique object list in Swift language like NSSet & NSMutableSet in Objective-C.

Answer 1

So I think creating a Set with an array is a terrible idea - O(n) is the time complexity of that set.

I have put together a nice Set that uses a dictionary: https://github.com/evilpenguin/Swift-Stuff/blob/master/Set.swift

Answer 2

Special case for classes derived from NSObject

given that default Equitable (& Hashable) conformance in NSObject is basically trash you'd better make sure you provide a proper

static func == (lhs: YourClassDerivedFromNSObject, rhs: YourClassDerivedFromNSObject) -> Bool {

implementation lest you want plucking the duplicates inserted into Set

Answer 3

I thought a struct with an internal Dictionary would be the way to go. I have only just started using it, so it’s not complete and I have no idea on performance yet.

struct Set<T : Hashable>
{
    var _items : Dictionary<T, Bool> = [:]

    mutating func add(newItem : T) {
        _items[newItem] = true
    }

    mutating func remove(newItem : T) {
        _items[newItem] = nil
    }

    func contains(item: T) -> Bool {
        if _items.indexForKey(item) != nil { return true } else { return false }
    }

    var items : [T] { get { return [T](_items.keys) } }
    var count : Int { get { return _items.count } }
}

Answer 4

I wrote a function to solve this problem.

public func removeDuplicates<C: ExtensibleCollectionType where C.Generator.Element : Equatable>(aCollection: C) -> C {
    var container = C()

    for element in aCollection {
        if !contains(container, element) {
            container.append(element)
        }
    }

    return container
}

To use it, just pass an array which contains duplicate elements to this function. And then it will return a uniqueness-guaranteed array.

You also can pass a Dictionary, String or anything conforms to ExtensibleCollectionType protocol if you like.

Answer 5

extension Array where Element: Hashable {
    var setValue: Set<Element> {
        return Set<Element>(self)
    }
}

let numbers = [1,2,3,4,5,6,7,8,9,0,0,9,8,7]
let uniqueNumbers = numbers.setValue    // {0, 2, 4, 9, 5, 6, 7, 3, 1, 8}

let names = ["John","Mary","Steve","Mary"]
let uniqueNames = names.setValue    // {"John", "Mary", "Steve"}