get distinct elements in an array by object property

Question

I have an array of object. I want to get distinct elements in this array by comparing objects based on its name property

class Item {
var name: String
init(name: String) {
    self.name = name
}
}
let items = [Item(name:"1"), Item(name:"2"), Item(name:"1"), Item(name:"1"),Item(name:"3"), Item(name:"4")]

result:

let items = [Item(name:"1"), Item(name:"2"),Item(name:"3"), Item(name:"4")]

how can I do this in swift?

Ciprian Rarau · Answer 1 · 2017-07-14T02:06:34.820

38

Here is an Array extension to return the unique list of objects based on a given key:

extension Array {
    func unique<T:Hashable>(by: ((Element) -> (T)))  -> [Element] {
        var set = Set<T>() //the unique list kept in a Set for fast retrieval
        var arrayOrdered = [Element]() //keeping the unique list of elements but ordered
        for value in self {
            if !set.contains(by(value)) {
                set.insert(by(value))
                arrayOrdered.append(value)
            }
        }

        return arrayOrdered
    }
}

For your example you can do:

let uniqueBasedOnName = items.unique{$0.name}

edited Jul 14 '17 at 02:06

answered Jul 11 '17 at 00:53

Ciprian Rarau

3,040
1
30
27

Thanks for that used it in the project then decided I only need to append unique data not remove it afterwards :) Added the answer at the end. – palme Mar 22 '21 at 19:03
1

Note that `by(value)` is calculated twice. If performance matters then assign the value to a variable and reuse – ULazdins Jan 12 '22 at 08:43
Can be improved - use just `if set.insert(by(value)).inserted {` and avoid calling `by(value)` twice. – Palli Mar 07 '22 at 10:11

score 4 · Accepted Answer · answered May 30 '16 at 05:17

4

Hope this will help you:

class Item:Equatable, Hashable {
    var name: String
    init(name: String) {
        self.name = name
    }
    var hashValue: Int{
      return name.hashValue
    }

}

func ==(lhs: Item, rhs: Item) -> Bool {
    return lhs.name == rhs.name
}


let items = [Item(name:"1"), Item(name:"2"), Item(name:"1"), Item(name:"1"),Item(name:"3"), Item(name:"4")]

var uniqueArray = Array(Set(items))

answered May 30 '16 at 05:17

Muzahid

5,072
2
24
42

this function `func ==(lhs: Item, rhs: Item) -> Bool {` is in global scope, is it ok? – Bista Jul 21 '17 at 10:32
Yes its ok @Bista – Muzahid Jul 21 '17 at 16:21

palme · Answer 3 · 2021-03-22T19:15:27.617

I used the sweet answer of @Ciprian Rarau and then realised I don't even need to add the elements in the first place if they are not unique. So I wrote a little extension for that (inspired by the answer).

extension Array {
    public mutating func appendIfUnique<T: Hashable>(_ newElement: Element, check property: ((Element) -> (T))) {
        for element in self {
            if property(element) == property(newElement) { return }
        }
        
        append(newElement)
    }
}

Append elements only if unique:

array.appendIfUnique(newElement, check: { $0.name })

score 0 · Answer 4 · answered Jul 01 '18 at 15:20

In Swift you can use Equatable protocol to distinguish unique element in an Array of object.

 struct Item:Equatable{
        var name:String
        var price:Double

        init(name:String,price:Double) {
            self.name = name
            self.price = price
        }

        static func ==(lhs: Item, rhs: Item) -> Bool{
            return lhs.name == rhs.name
        }
    }

    class ViewController: UIViewController {

       var books = [Item]()
        override func viewDidLoad() {
            super.viewDidLoad()
            items.append(Item(name: "Example 1", price: 250.0))
            items.append(Item(name: "Example 2", price: 150.0))
            items.append(Item(name: "Example 1", price: 150.0))
            items.append(Item(name: "Example 1", price: 150.0))
            items.append(Item(name: "Example 3", price: 100.0))
            items.unique().forEach { (item) in
                print(item.name)
            }
        }

    }

    extension Sequence where Iterator.Element: Equatable {
        func unique() -> [Iterator.Element] {
            return reduce([], { collection, element in collection.contains(element) ? collection : collection + [element] })
        }
    }

mikro098 · Answer 5 · 2022-03-30T19:51:29.127

Solution that uses keypaths instead of closures:

extension Sequence {
    func uniqued<Type: Hashable>(by keyPath: KeyPath<Element, Type>) -> [Element] {
        var set = Set<Type>()
        return filter { set.insert($0[keyPath: keyPath]).inserted }
    }
}

Example for struct Mock { var uuid: UUID; var num: Int }

let uuid = UUID()
let arr = [
    Mock(uuid: uuid, num: 1),
    Mock(uuid: uuid, num: 2),
    Mock(uuid: UUID(), num: 3)
]

let unique = arr.uniqued(by: \.uuid)

unique array will contain first (num = 1) and last (num = 3) elements.

get distinct elements in an array by object property

5 Answers5