Swift：来自键和值数组的字典

Question

我需要转换一组键和值，例如：

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

进入字典：

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

我可以 go 通过数组一步两步，分别获得键和值的 n 和 n+1，但是有什么聪明的方法吗？

谢谢！

Answer 1

您可以将您的集合分成两个子序列并将它们减少到字典中：

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"]

---

另一种使用步幅的方法。 这假设您的集合具有偶数个元素：

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"]