ios - Swift 减少/展平 Dictionary 到 Dictionary

Question

Convert this

[ 
   "Cat" : ["A" : 1, "B": 2], 
   "Mat" : ["C" : 3, "D": 4]
]

Into

[
    "A" : 1, 
    "B" : 2,
    "C" : 3,
    "D" : 4
]

不使用循环。换句话说，使用 reduce、flatmap 等函数。

source可以是类型 Dictionary<String,Dictionary<String,String>>

---

到目前为止，我已经设法将 Dictionary 缩减为一个 Dictionary 数组

let flatten = source.flatMap({ (k,v) -> [String: String]? in
                            return v
                        })

// flatten = [["A" : 1, "B": 2], ["C" : 3, "D": 4]]]

Answer 1

一个选项:

let dictionary = [
    "Cat" : ["A" : 1, "B": 2],
    "Mat" : ["C" : 3, "D": 4]
]

let merged = dictionary
   // take values, we don't care about keys
   .values
   // merge all dictionaries
   .reduce(into: [:]) { (result, next) in
      result.merge(next) { (_, rhs) in rhs }
   }
print(merged) // ["B": 2, "A": 1, "C": 3, "D": 4]