Unique Objects inside a Array Swift

Question

I have an array, with custom objects.

I Would like to pop the repeated objects, with the repeated properties:

let product = Product()
product.subCategory = "one"

let product2 = Product()
product2.subCategory = "two"

let product3 = Product()
product3.subCategory = "two"

let array = [product,product2,product3]

in this case, pop the product2 or product3

Answer 1

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

extension Array {
    func unique<T:Hashable>(map: ((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(map(value)) {
                set.insert(map(value))
                arrayOrdered.append(value)
            }
        }

        return arrayOrdered
    }
}

using this you can so this

let unique = [product,product2,product3].unique{$0.subCategory}

this has the advantage of not requiring the Hashable and being able to return an unique list based on any field or combination

Answer 2

Here is a KeyPath based version of the Ciprian Rarau' solution

extension Array {
    func unique<T: Hashable>(by keyPath: KeyPath<Element, T>) -> [Element] {
        var set = Set<T>()
        return self.reduce(into: [Element]()) { result, value in
            guard !set.contains(value[keyPath: keyPath]) else {
                return
            }
            set.insert(value[keyPath: keyPath])
            result.append(value)
        }
    }
}

example usage:

let unique = [product, product2, product3].unique(by: \.subCategory)

Answer 3

If Product conforms to Equatable, where a product is equal based on it's subcategory (and you don't care about order), you can add the objects to a set, and take an array from that set:

let array = [product,product2,product3]
let set = NSSet(array: array)
let uniqueArray = set.allObjects

or

let array = [product,product2,product3]
let set = Set(array)
let uniqueArray = Array(set)