[Swift5]配列と配列の差集合を取得する方法

方法

(array1 - array2　を実行する場合を考えます。)

1. array1とarray2を結合してSetに変換
2. 1の結果からarray2の要素を取り除く

コード

let array1 = ["a", "b", "c", "d", "e"]
let array2 = ["a", "c", "e"]

let unionSet = Set(array1 + array2)
let diffArray = Array(unionSet.subtracting(array2))
print(diffArray)
// ["b", "d"]

自作した構造体に対しても同じように実行できます。

struct Food: Hashable {
    //Hashableのプロトコルメソッド
    static func == (lhs: Food, rhs: Food) -> Bool {
        return (lhs.name == rhs.name) && (lhs.price == rhs.price)
    }

    let name: String
    let price: Int
}

let food1 = Food(name: "ラーメン", price: 800)
let food2 = Food(name: "うどん", price: 700)
let food3 = Food(name: "そば", price: 600)

let myFavoriteFood = [food1, food2, food3]
let yourFavoriteFood = [food1]

let unionSet = Set(myFavoriteFood + yourFavoriteFood)
let diffArray = Array(unionSet.subtracting(yourFavoriteFood))
print(diffArray[0], diffArray[1])
// Food(name: "うどん", price: 700) Food(name: "そば", price: 600)