如何在Swift 5中擴展Dict（string，array）

Question

我可以使用map/reduce將字典擴展為Swift 5中的成對數組嗎？還是必須for each字典做一個？

let dict = ["A": ["1","2","3","4"],
            "B": ["5","6","7","8"]]

???

//result = [["A", "1"],["A", "2"],....["B", "5"],....]

Answer 1

let result = dict.map { (letter: String, digits: [String]) in
    return digits.map { digit in
        return [letter, digit]
    }
}.reduce([]) {
    $0 + $1
}

Answer 2

這是最短的解決方案。

let result = dict.map { dic in
        dic.value.map { [dic.key : $0] }
    }.reduce([], +) 

Answer 3

這是不需要reduce的解決方案：

let dict = ["A": ["1","2","3","4"],
            "B": ["5","6","7","8"]]
let result = dict.map { kv in kv.value.map { [kv.key, $0] } }.flatMap { $0 }