Swift：for循环，搜索字典，从键设置变量答案

【问题标题】：Swift: for loop, search dictionary, set variables from keysSwift：for循环，搜索字典，从键设置变量
【发布时间】：2016-06-18 21:23:52
【问题描述】：

错误是：无法转换类型（字符串：Int）的值？到指定类型“字符串”。

显然，我的字典 'roster' 是 'String: Int' 而函数 'printRoster' 中的局部变量（'lastPlayer' 和 'firstPlayer'）是 String。但是我已经尝试了所有变体，但没有运气。在我制作 roster 字典之前它工作得很好，它只是一个字符串。

它应该做什么：函数连接一个字符串，使其具有正确的标点符号。第一个字符串是“名册包括”，然后我们添加位于字典“名册”键中的每个玩家。但是花名册中的第一个键没有逗号，最后一个键有一个 ', and'。

另外，我可以将字典“名册”添加到协议中吗，在任何 Apple 手册中都没有看到语法

    import UIKit

protocol basketballTeams {
    var teamName: String? { get }
    var numberOfPlayers: Int? { get }
    var locatedIn: String? { get }

    func printTeamLocation()
}

class BasketballTeam {
    var teamName: String?
    var numberOfPlayers: Int?
    var locatedIn: String?
    var roster = [String: Int]()

    init(teamName: String) {
        self.teamName = teamName
    }

    func printTeamLocation() -> String {
        return "The \(teamName) are located in \(locatedIn)"
    }
    func printRoster() -> String {
        var rosterPrint = "The roster includes"
        for player in roster.keys {

            rosterPrint += player

            var firstPlayer: String = roster.first
            var lastPlayer = roster.last

            if (player == firstPlayer) {
                rosterPrint += " \(player)"
            }
            else if (player == lastPlayer) {
                rosterPrint += ", and \(player)."
            }
            else {
            rosterPrint += ", \(player)"
            }
        }
        return rosterPrint
    }
}

enum NumberedPosition: Int {
    case PointGuard = 1
    case ShootingGuard, SmallForward, PowerForward, Center
    func labelOfPosition() -> String {
        switch self {
        case .PointGuard:
            return "Point Guard"
        case .ShootingGuard:
            return "Shooting Guard"
        case .SmallForward:
            return "Small Forward"
        case .PowerForward:
            return "Power Forward"
        case .Center:
            return "Center"
        default:
            "Position doesn't exit"
        }
    }
}

let goldenStateWarriors = BasketballTeam(teamName: "Golden State Warriors")
goldenStateWarriors.numberOfPlayers = 12
goldenStateWarriors.locatedIn = "Oakland, California"
goldenStateWarriors.roster = ["Stephen Curry" : 1, "Andrew Bogut" : 5, "Klay Thompson" : 2]
goldenStateWarriors.roster["Harrison Barnes"] = 3

【问题讨论】：

标签： swift string dictionary

【解决方案1】：

这个怎么样：

let roster = ["Stephen Curry":1, "Andrew Bogu": 2, "Klay Thompson":3]

let players = roster.keys.joined(separator: ", ")
let all = "Roster contains: \(players)."

【讨论】：

比我的解决方案更好，恭喜！但是请注意，在 Swift 2.2 中，正确的语法仍然是 joinWithSeparator
虽然这可行，但它似乎没有我正在寻找的动态。我希望完全正确的语法和 for 循环能够工作，这样我就可以构建更高级的功能。因为我接下来要做的就是将值与枚举器联系起来。

【解决方案2】：

如果您仍想在最后一行添加“and”，您可以使用此功能：

func printRoster() -> String {
  var rosterPrint = "The roster includes"
  let arr = Array(roster.keys)
  let firstPlayer: String = arr.first!
  let lastPlayer: String = arr.last!
  for (player, _ ) in roster {
    switch player {
    case firstPlayer:
      rosterPrint += " \(player)"
    case lastPlayer:
      rosterPrint += ", and \(player)."
    default:
      rosterPrint += ", \(player)"
    }
   }
   return rosterPrint
}

然后这样称呼它：

print(goldenStateWarriors.printRoster())

【讨论】：

好的，所以基本上swift不会让我对字典进行操作，我必须将键复制到重复的数组中，然后我可以做到。如果是这种情况，他们有可能在 3.0 中解决这个问题吗？
是的，roster.keys 返回一个LazyMapCollection，它不能用Int 进行索引并且没有last 方法，因此复制到数组允许您使用last方法来设置lastPlayer。编辑我认为它不会被修复，仅仅是因为它没有被破坏。 LazyMapCollection 允许更好地访问大型字典。 @JamesGoldstein
'.count - 1' 可以在不复制到数组的情况下工作吗？
不幸的是，LazyMapCollections 不能被 Int 值索引，它们使用自己的索引类型。看这里：developer.apple.com/reference/swift/lazymapcollection@JamesGoldstein
太棒了！效果很好

【解决方案3】：

鉴于这本词典

let roster = ["Stephen Curry":1, "Andrew Bogu": 2, "Klay Thompson":3]

你可以

let elms = roster
    .keys
    .reduce("") { $0.1 + ", " + $0.0 }
    .characters
    .dropLast()
    .dropLast()

let res = "The roster includes " + String(elms)

结果

"The roster includes Andrew Bogu, Stephen Curry, Klay Thompson"

更新 #1：使用 FOR 循环

既然你想使用 for 循环，这里是代码

let roster = ["Stephen Curry":1, "Andrew Bogu": 2, "Klay Thompson":3]
var result = "The roster includes "
for (index, elm) in roster.keys.enumerate() {
    result += elm
    if index < roster.keys.count - 1 {
        result += ", "
    }
}

print(result) // The roster includes Klay Thompson, Stephen Curry, Andrew Bogu

更新 #2：将 FOR LOOP 与 first 和 last 一起使用

let roster = ["Stephen Curry":1, "Andrew Bogu": 2, "Klay Thompson":3]

func printRoster() -> String {

    var rosterPrint = "The roster includes"
    let players = Array(roster.keys)


    guard let
        first = players.first,
        last = players.last
        else { return "" } // this is ugly, it should return nil instead...

    for player in players {
        switch player {
        case first: rosterPrint += " \(player)"
        case last: rosterPrint += ", and \(player)."
        default: rosterPrint += ", \(player)"
        }
    }
    return rosterPrint
}

printRoster() // "The roster includes Klay Thompson, Stephen Curry, and Andrew Bogu."

【讨论】：

也比我想要的更简单。我希望保留 for 循环。语法也要正确。
@JamesGoldstein：我添加了 FOR LOOP 实现
谢谢，但我认为像上面一样使用更新的 Swift 函数 .first 和 .last 可能会更好。
实际上，也许不是。看起来我可以将键复制到数组中并将我的代码与“.last”或“.first”一起使用，或者我可以保存复制步骤并使用“.count - 1”。
@JamesGoldstein：刚刚又更新了我的答案，请看一下

【解决方案4】：

这似乎运作良好，至少在他们允许 .first 和 .last 使用字典之前（如果可能的话）。

    class BasketballTeam {
    var teamName: String?
    var numberOfPlayers: Int?
    var locatedIn: String?
    var roster = [String: Int]()

    init(teamName: String) {
        self.teamName = teamName
    }

    func printTeamLocation() -> String {
        return "The \(teamName) are located in \(locatedIn)"
    }
    func printRoster() -> String {
        var rosterPrint = "The roster includes"
        let rosterArray = Array(roster.keys)

        for player in rosterArray {

            let firstPlayer = rosterArray.first
            let lastPlayer = rosterArray.last

            switch player {
            case firstPlayer!:
                rosterPrint += " \(player)"
            case lastPlayer!:
                rosterPrint += ", and \(player)."
            default:
                rosterPrint += ", \(player)"
            }
        }
        return rosterPrint
    }
}

完整代码，如果您想快速学习并熟悉篮球，可以粘贴到游乐场

import UIKit

protocol basketballTeams {
    var teamName: String { get }
    var numberOfPlayers: Int { get }
    var locatedIn: String { get }
    var roster: [String: Int] { get }

    func printTeamLocation()
}

class BasketballTeam {
    var teamName: String?
    var numberOfPlayers: Int?
    var locatedIn: String?
    var roster = [String: Int]()

    init(teamName: String) {
        self.teamName = teamName
    }

    func printTeamLocation() -> String {
        return "The \(teamName) are located in \(locatedIn)"
    }
    func printRoster() -> String {
        var rosterPrint = "The roster includes"
        let rosterArray = Array(roster.keys)

        for player in rosterArray {

            let firstPlayer = rosterArray.first
            let lastPlayer = rosterArray.last

            switch player {
            case firstPlayer!:
                rosterPrint += " \(player)"
            case lastPlayer!:
                rosterPrint += ", and \(player)."
            default:
                rosterPrint += ", \(player)"
            }
        }
        return rosterPrint
    }
}

enum NumberedPosition: Int {
    case PointGuard = 1
    case ShootingGuard, SmallForward, PowerForward, Center
    func labelOfPosition() -> String {
        switch self {
        case .PointGuard:
            return "Point Guard"
        case .ShootingGuard:
            return "Shooting Guard"
        case .SmallForward:
            return "Small Forward"
        case .PowerForward:
            return "Power Forward"
        case .Center:
            return "Center"
        default:
            "Position doesn't exist"
        }
    }
}

let goldenStateWarriors = BasketballTeam(teamName: "Golden State Warriors")
goldenStateWarriors.numberOfPlayers = 12
goldenStateWarriors.locatedIn = "Oakland, California"
goldenStateWarriors.roster = ["Stephen Curry" : 1, "Andrew Bogut" : 5, "Klay Thompson" : 2]
goldenStateWarriors.roster["Harrison Barnes"] = 3

goldenStateWarriors.printRoster()
goldenStateWarriors.printTeamLocation()

var num = 3

if let numberToPositionConv = NumberedPosition(rawValue: num) {
    let description = numberToPositionConv.labelOfPosition()
}

【讨论】：