Swift 字典过滤器

Question

所以看起来 Swift (2.x) 字典上的过滤器函数返回一个元组数组。我的问题是有一个优雅的解决方案可以把它变成字典吗？提前致谢。

let dictionary: [String: String] = [
    "key1": "value1",
    "key2": "value2",
    "key3": "value3"
]

let newTupleArray: [(String, String)] = dictionary.filter { (tuple: (key: String, value: String)) -> Bool in
    return tuple.key != "key2"
}

let newDictionary: [String: String] = Dictionary(dictionaryLiteral: newTupleArray) // Error: cannot convert value of type '[(String, String)]' to expected argument type '[(_, _)]'

Answer 1

如果您正在寻找更实用的方法：

let result = dictionary.filter {
        $0.0 != "key2"
    }
    .reduce([String: String]()) { (var aggregate, elem) in
        aggregate[elem.0] = elem.1
        return aggregate
    }

reduce 这里用于从过滤后的元组构造一个新字典。

---

编辑：由于 Swift 2.2 中已弃用 var 参数，您需要创建 aggregate 的本地可变副本：

let result = dictionary.filter {
        $0.0 != "key2"
    }
    .reduce([String: String]()) { aggregate, elem in
        var newAggregate = aggregate
        newAggregate[elem.0] = elem.1
        return newAggregate
    }

Answer 2

您可以扩展 Dictionary 以便将元组序列作为初始值：

extension Dictionary {
  public init<S: SequenceType where S.Generator.Element == (Key, Value)>(_ seq: S) {
      self.init()
      for (k, v) in seq { self[k] = v }
  }
}

然后做

let newDictionary = Dictionary(newTupleArray)