ios - 快速过滤和排序字典数组

Question

我有以下数组:

let parent = [ ["Step":"S 3", "Desc":"Do third step" ],
               ["Step":"S 1", "Desc":"Do first step" ],
               ["Step":"S 2", "Desc":"Do second step" ],
                ["Step":"P 1", "Desc":"Some other thing" ] ]

如何以尽可能少的步骤对数组进行过滤和排序(使用过滤和排序函数)，以便获得以下输出字符串或标签 --

1.做第一步

2.做第二步

3.做第三步

Answer 1

我建议过滤、排序、枚举、映射和连接:

let results = parent
    .filter { $0["Step"]?.first == "S" }
    .sorted { $0["Step"]!.compare($1["Step"]!, options: .numeric) == .orderedAscending }
    .enumerated()
    .map { (index, value) in "\(index + 1). \(value["Desc"]!)" }
    .joined(separator: "\n")

一个关键的考虑因素是使用 .numeric 比较，这样“S 10”就会出现在“S 9”之后，而不是在“S 1”和“S 2”之间。如果要在字符串中嵌入数值，您不想进行简单的字符串比较。

我还加入了那个枚举，因为如果你删除了一个项目，你可能想确保你的列表中的数字不会仅仅因为你的 Step 中的特定编码而跳过一个值> 字符串。

---

不相关，字典对于这样的事情来说是一个糟糕的模型。我建议使用自定义类型:

struct Task {
    enum TaskType {
        case step
        case process    // or whatever "P" is supposed to stand for
    }

    let sequence: Int
    let type: TaskType
    let taskDescription: String
}

let parent = [Task(sequence: 3, type: .step, taskDescription: "Do third step"),
              Task(sequence: 1, type: .step, taskDescription: "Do first step"),
              Task(sequence: 2, type: .step, taskDescription: "Do second step"),
              Task(sequence: 3, type: .process, taskDescription: "Some other thing")]

let results = parent
    .filter { $0.type == .step }
    .sorted { $0.sequence < $1.sequence }
    .map { "\($0.sequence). \($0.taskDescription)" }
    .joined(separator: "\n")