Swift：來自鍵和值數組的字典

Question

我需要轉換一組鍵和值，例如：

["key1", "value1", "key2", "value2"]

進入字典：

{"key1": "value1", "key2": "value2"}

我可以 go 通過數組一步兩步，分別獲得鍵和值的 n 和 n+1，但是有什么聰明的方法嗎？

謝謝！

Answer 1

您可以將您的集合分成兩個子序列並將它們減少到字典中：

extension Collection {
    func unfoldSubSequences(limitedTo maxLength: Int) -> UnfoldSequence<SubSequence,Index> {
        sequence(state: startIndex) { start in
            guard start < self.endIndex else { return nil }
            let end = self.index(start, offsetBy: maxLength, limitedBy: self.endIndex) ?? self.endIndex
            defer { start = end }
            return self[start..<end]
        }
    }
}

---

let kvs = ["key1", "value1", "key2", "value2"]

let dictionary = kvs
    .unfoldSubSequences(limitedTo: 2)
    .reduce(into: [:]) {
        guard $1.count == 2, let key = $1.first, let value = $1.last else { return }
        $0[key] = value
    }
dictionary  // ["key1": "value1", "key2": "value2"]

---

另一種使用步幅的方法。 這假設您的集合具有偶數個元素：

let kvs = ["key1", "value1", "key2", "value2"]

let dictionary = stride(from: 0, to: kvs.count, by: 2)
    .reduce(into: [:]) { $0[kvs[$1]] = kvs[$1+1] }
dictionary  // ["key1": "value1", "key2": "value2"]