如何从 swift 中的键值对（元组）序列创建一个双字符串数组

Question

我有两个字符串数组，它定义如下如何从一系列键值对创建字典。

let cityNames = ["Riyadh", "Mecca", "Sultanah", "Buraydah", "Al Qarah"]
let nearestDistances = [84.24, 41.37, 45.37, 57.96, 78.78]

如有任何帮助，我们将不胜感激。

Answer 1

只需zip将它们组合成一个循环

var dictionary = [String: Double]()

for (city, distance) in zip(cityNames, nearestDistances){
    dictionary[city] = distance
}

更好的是，你可以为它做一个很好的扩展：

extension Dictionary{
    init(keys: [Key], values: [Value]){
        self.init()
        for (key, value) in zip(keys, values){
            self[key] = value
        }
    }
}

let dictionary = Dictionary<String, Double>(keys: cityNames, values: nearestDistances)

Answer 2

如前所述，自 Xcode 9 起，Swift 标准库 为此类情况提供了方便的 Dictionary initializer：

init<S>(uniqueKeysWithValues keysAndValues: S) 
where S: Sequence, S.Element == (Key, Value)

Creates a new dictionary from the key-value pairs in the given sequence.

如果不太熟悉 Swift 泛型，这可能难以阅读；）不过，用法非常简单：

let cityNames = ["Riyadh", "Mecca", "Sultanah", "Buraydah", "Al Qarah"]
let nearestDistances = [84.24, 41.37, 45.37, 57.96, 78.78]

let dict = Dictionary(uniqueKeysWithValues: zip(cityNames, nearestDistances))
print(dict)

打印：

[  
  "Buraydah": 57.96, 
  "Al Qarah": 78.78, 
  "Mecca":    41.37, 
  "Riyadh":   84.24, 
  "Sultanah": 45.37
]

最后，生成的字典类型就是您所期望的：

print(type(of: dict)) // Dictionary<String, Double>

如何从 swift 中的键值对（元组）序列创建一个双字符串数组

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