Swift 等价于 `[NSDictionary initWithObjects: forKeys:]` [英] Swift equivalent to `[NSDictionary initWithObjects: forKeys:]`

问题描述

Swift 的原生 Dictionary 是否有与 [NSDictionary initWithObjects: forKeys:] 等效的东西?

Is there an equivalent for Swift's native Dictionary to [NSDictionary initWithObjects: forKeys:]?

假设我有两个带有键和值的数组，并想将它们放入字典中.在 Objective-C 中，我会这样做:

Say I have two arrays with keys and values and want to put them in a dictionary. In Objective-C I'd do it like this:

NSArray *keys = @[@"one", @"two", @"three"];
NSArray *values = @[@1, @2, @3];
NSDictionary *dict = [[NSDictionary alloc] initWithObjects: values forKeys: keys];

当然，我可以使用计数器遍历两个数组，使用 var dict: [String:Int] 并逐步添加内容.但这似乎不是一个好的解决方案.使用 zip 和 enumerate 可能是同时迭代两者的更好方法.然而，这种方法意味着拥有一个可变的字典，而不是一个不可变的字典.

Of course I can iterate with a counter through both arrays, use a var dict: [String:Int] and add stuff step by step. But that doesn't seem to be a good solution. Using zip and enumerate are probably better ways of iterating over both at the same time. However this approach means having a mutable dictionary, not an immutable one.

let keys = ["one", "two", "three"]
let values = [1, 2, 3]
// ???
let dict: [String:Int] = ["one":1, "two":2, "three":3] // expected result

推荐答案

从 Swift 4 开始，您可以直接从键/值对序列:

As of Swift 4 you can create a dictionary directly from a sequence of key/value pairs:

let keys = ["one", "two", "three"]
let values = [1, 2, 3]

let dict = Dictionary(uniqueKeysWithValues: zip(keys, values))

print(dict) // ["one": 1, "three": 3, "two": 2]

这里假设所有key都不一样，否则会中止有运行时异常.

This assumes that all keys are different, otherwise it will abort with a runtime exception.

如果不能保证键是不同的，那么你可以这样做

If the keys are not guaranteed to be distinct then you can do

let keys = ["one", "two", "one"]
let values = [1, 2, 3]

let dict = Dictionary(zip(keys, values), uniquingKeysWith: { $1 })

print(dict) // ["one": 3, "two": 2]

第二个参数是一个闭包，它决定了哪个值获胜"在重复键的情况下.

The second argument is a closure which determines which value "wins" in the case of duplicate keys.

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