Question

为什么我不能返回字典countDict，如下所示：

我收到错误：

错误：无法转换类型'[（key：String，value： Int）]'返回类型'[String：Int]' return countDict.sorted（by：{$ 0.value＆gt; $ 1.value}）

码：

let arr = ["red","green","green","black","blue","yellow","red","green","yellow","red","red","green"
            ,"green","grey","purple","orange","grey","blue","red","red","green","yellow","orange","purple","black","red"
            ,"blue","green","orange","blue","blue","white","yellow","blue","red","green","orange","purple","blue","black"]


func mostFrequentColor(arr: [String]) -> [String: Int] {
    guard arr.count != 0 else {return [:]}

    var countDict = [String: Int]()

    for color in arr {
        countDict[color] = (countDict[color] ?? 0) + 1
    }
    return countDict.sorted(by: { $0.value > $1.value })
}

print(mostFrequentColor(arr: arr))

Answer 1

字典按定义未排序，因此Dictionary.sorted(by:)实际上返回一个元组数组（由Dictionary中存储的键值对组成，因此错误。如果你密切关注什么是错误说，您会看到您尝试返回的类型为[(key: String, val: Int)]，这是Array<(String,Int)>的简写，而不是预期类型[String:Int]，这是Dictionary<String,Int>的简写。

您只需删除排序即可解决错误。如果您确实需要对颜色进行排序，则需要使用其他数据结构，因为Dictionary按定义未排序。

您也不需要guard声明，因为您无论如何都要将countDict设为空Dictionary，而for ... in循环只是赢得了arr。如果func mostFrequentColor(arr: [String]) -> [String: Int] { var countDict = [String: Int]() for color in arr { countDict[color, default: 0] += 1 } return countDict }没有元素，则执行t。修改Dictionary的值时，也可以使用简写语法。

func mostFrequentColor(arr: [String]) -> [String: Int] {
    return colors.reduce(into: [String:Int](), { accumulatedResult, currentColor in
        accumulatedResult[currentColor, default: 0] += 1
    })
}

mostFrequentColor(arr: colorsArray) //["red": 8, "blue": 7, "grey": 2, "white": 1, "green": 8, "black": 3, "orange": 4, "purple": 3, "yellow": 4]

使用更实用的方法，您的功能实际上可以缩短为：

<form method="POST" action="/">    
   <input type="submit" name="Click">

使用Swift中[String：Int]类型的简写返回字典

1 个答案: