Swift：将一组字典展平为一个字典

Swift: Flatten an array of dictionaries to one dictionary

在 Swift 中，我正在尝试将一组字典扁平化为一个字典
即

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let arrayOfDictionaries = [["key1":"value1"], ["key2":"value2"], ["key3":"value3","key4":"value4"]]

//the end result will be:
flattenedArray = ["key1":"value1","key2":"value2","key3":"value3","key4":"value4"]

我尝试过使用flatmap，但是返回结果的类型是[(String, AnyObject)] 而不是[String, Object] 即

1 2	let flattenedArray = arrayOfDictionaries.flatMap { $0 } // type is [(String, AnyObject)]

所以我有两个问题：

为什么返回类型[(String, AnyObject)]？括号是什么意思？
我怎样才能达到预期的效果？

编辑：我更喜欢使用 Swift 的 map/flatmap/reduce 等功能方法，而不是 for-loop

what do the brackets mean?

这与逗号而不是冒号一起应该提供第一个线索：括号意味着你得到一个元组数组。由于您要查找的是字典，而不是数组，这告诉您需要将元组序列(键值对)转换为单个字典。

How do I achieve the desired result?

一种方法是使用 reduce，如下所示：

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let flattenedDictionary = arrayOfDictionaries
.flatMap { $0 }
.reduce([String:String]()) { (var dict, tuple) in
dict.updateValue(tuple.1, forKey: tuple.0)
return dict
}

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在 Swift 5 中，Dictionay 有一个 init(_:uniquingKeysWith:) 初始化器。 init(_:uniquingKeysWith:) 具有以下声明：

1	init(_ keysAndValues: S, uniquingKeysWith combine: (Value, Value) throws -> Value) rethrows where S : Sequence, S.Element == (Key, Value)

Creates a new dictionary from the key-value pairs in the given sequence, using a combining closure to determine the value for any duplicate keys.

以下两个 Playground 示例代码展示了如何将字典数组展平为新字典。

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let dictionaryArray = [["key1":"value1"], ["key1":"value5","key2":"value2"], ["key3":"value3"]]

let tupleArray: [(String, String)] = dictionaryArray.flatMap { $0 }
let dictonary = Dictionary(tupleArray, uniquingKeysWith: { (first, last) in last })

print(dictonary) // prints ["key2":"value2","key3":"value3","key1":"value5"]

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let dictionaryArray = [["key1": 10], ["key1": 10,"key2": 2], ["key3": 3]]

let tupleArray: [(String, Int)] = dictionaryArray.flatMap { $0 }
let dictonary = Dictionary(tupleArray, uniquingKeysWith: { (first, last) in first + last })
//let dictonary = Dictionary(tupleArray, uniquingKeysWith: +) // also works

print(dictonary) // ["key2": 2,"key3": 3,"key1": 20]

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更新@dasblinkenlight 对 Swift 3 的回答。

参数中的"var"已被弃用，但这种方法对我来说效果很好。

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let flattenedDictionary = arrayOfDictionaries
.flatMap { $0 }
.reduce([String:String]()) { (dict, tuple) in
var nextDict = dict
nextDict.updateValue(tuple.1, forKey: tuple.0)
return nextDict
}

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这里是做

的方法

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let arrayOfDictionaries = [["key1":"value1"], ["key2":"value2"], ["key3":"value3","key4":"value4"]]
var dic = [String: String]()
for item in arrayOfDictionaries {
for (kind, value) in item {
print(kind)
dic.updateValue(value, forKey: kind)
}

}
print(dic)

print(dic["key1"]!)

OUTPUT

OUTPUT

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