swift - 从 Array> 中提取字符串数组的有效方法

Question

是否有一种有效的方法可以在不使用嵌套 for 循环的情况下从下面的 AllData 中获取包含“名称”字符串的数组？我得到的代码有效:“Alice”、“Brad Smith MD”、“Dr. Quam”、“Jennifer Johnson”、“John Banks MD”作为输出，但我想在没有嵌套 for 循环的情况下执行它，因为它效率不高O n^2 并且很难阅读？我在 Xcode 8.2 中使用 Swift 3

 var AllData:Array<Dictionary<String,String>> = []

 override func viewDidLoad() {
         super.viewDidLoad()

    AllData = [["pic":"Alice.png","name":"Alice Smith","position":"Nurse"],
               ["pic":"brad.png","name":"Brad Smith MD","position":"Primary Doctor"],
               ["pic":"user.png","name":"Dr. Quam","position":"Immunologist"],
               ["pic":"jennifer.jpg","name":"Jennifer Johnson","position":"Case Manager"],
               ["pic":"user.png","name":"John Banks MD","position":"Cardiologist"]
               ]

let names = ""

for thing in AllData { //thing is pic, name, position

                    for (key, value) in thing {
                        if(key == "name"){
                            names.append(value)
                            //print(value)
                        }
                    }
                }

 print(names)
}

Answer 1

绝对没有理由遍历字典中的一组 (key, value) 对，比较键直到找到特定的匹配项，只使用值。直接下标字典即可:

var names = ""
for dict in AllData { //thing is pic, name, position
    guard let name = dict["name"] else { continue }
    names.append(name)
}
print(names)

函数式方法更快更简单:

let names = AllData.flatMap{ $0["name"] }.joined(separator: "")

此外，您不应该使用 Dictionary 来存储具有一组静态键的数据。如果您使用结构或类来封装数据，您将拥有更简单、更快速且类型更安全的代码。最终结果看起来像这样:

struct Employee {
    let pic: String
    let name: String
    let position: Sting //TODO: would this be better as an enum?
}


class MyVC: UIViewController {
    //...

    let employees = [
        Employee(
            pic: "Alice.png",
            name: "Alice Smith",
            position: "Nurse"
        ),
        Employee(
            pic: "brad.png",
            name: "Brad Smith MD",
            position: "Primary Doctor"
        ),
        Employee(
            pic: "user.png",
            name: "Dr. Quam",
            position: "Immunologist"
        ),
        Employee(
            pic: "jennifer.jpg",
            name: "Jennifer Johnson",
            position: "Case Manager"
        ),
        Employee(
            pic: "user.png",
            name: "John Banks MD",
            position: "Cardiologist"
        )
    ]

    override func viewDidLoad() {
        super.viewDidLoad()

        let names = employees.map{ $0.name }.joined(separator: "")

        print(names)
    }

    //...
}

dict 和 struct 方法都是 O(employees.count)，但是 struct 方法的开销更低，样板代码更少，并且可以让您轻松处理非 String 员工数据。