如何在 Swift 中找到字典的平均值？

Question

我有一本字典，比如说

let gamePrices = [
"Shooter": [40,60,80],
"RTS": [15,35,55]
"RPG": [5,40,70]
]
avgGamePrices(dictionary: [String: Int]) -> Double {
var total = 0;
for int in dictionary {
total += int
} 

（我想，这里使用 int 是错误的） 而且我不明白如何获得每种类型的平均价格和总平均价格（所有 9 个值）。我什至不知道如何在这里获取总数，我应该如何在 for 循环中“提及”字典的整数或字符串？ 对于默认数组，我会使用

for number in numbers {
total += number
}
let numbersTotal = Int(numbers.count);
let average = total/numbersTotal;
return (Double(average);

Answer 1

要获取所有价格的平均值，您需要先从字典中获取所有价格，然后才能计算平均值。与计算平均值的平均值不同：

let gamePrices = [
    "Shooter": [40,60,80],
    "RTS":     [15,35,55],
    "RPG":     [5,40,70]]

let allPrices = gamePrices.flatMap(\.value)
let sum = allPrices.reduce(.zero, +)
let average = Double(sum) / Double(allPrices.count)  //  44.44444444444444

要获得每种类型的最高价格：

let maxPrices: [(genre: String, maxPrice: Int)] = gamePrices.map { ($0, $1.max() ?? .zero)}  // [(genre "Shooter", maxPrice 80), (genre "RTS", maxPrice 55), (genre "RPG", maxPrice 70)]

for (genre, max) in maxPrices {
    print("Genre:", genre, "Max price:", max)
}

Answer 2

如果您搜索总 AVG，则如下所示：

func avgGamePrices(dictionary: [String: [Int]]) -> Double {
var total = 0;
var countElem = 0

for obj in dictionary {
    countElem += obj.value.count
    for v in obj.value {
        total += v
    }
}

return Double(total / countElem)

}

调用：

avgGamePrices(dictionary: gamePrices)

否则对于每个键：

func avg(for key: String, dictionary: [String: [Int]]) -> Double {
var total = 0;
let countElem = (dictionary[key] ?? []).count

for v in (dictionary[key] ?? []) {
    total += v
}

return Double(total / countElem)

}

您可以通过这种方式调用（像参数一样传递字典的单个键）：

avg(for: "RTS", dictionary: gamePrices)