使我的函数计算数组Swift的平均值

Question

我希望函数计算Double型数组的平均值。该数组称为“投票”。现在，我有10个号码。

当我致电average function以获取阵列投票的平均值时，它不起作用。

这是我的代码：

var votes = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]

func average(nums: Double...) -> Double {
    var total = 0.0
    for vote in votes {
        total += vote
    }
    let votesTotal = Double(votes.count)
    var average = total/votesTotal
    return average
}

average[votes]

我如何在此处称平均值以获得平均值？

Answer 1

您应该使用reduce（）方法对数组求和，如下所示：

Xcode Xcode 10.2+•Swift 5或更高版本

extension Sequence where Element: AdditiveArithmetic {
    /// Returns the total sum of all elements in the sequence
    func sum() -> Element { reduce(.zero, +) }
}

extension Collection where Element: BinaryInteger {
    /// Returns the average of all elements in the array
    func average() -> Element { isEmpty ? .zero : sum() / Element(count) }
    /// Returns the average of all elements in the array as Floating Point type
    func average<T: FloatingPoint>() -> T { isEmpty ? .zero : T(sum()) / T(count) }
}

extension Collection where Element: BinaryFloatingPoint {
    /// Returns the average of all elements in the array
    func average() -> Element { isEmpty ? .zero : Element(sum()) / Element(count) }
}

let votes = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
let votesTotal = votes.sum()                       // 55
let votesAverage = votes.average()                 // 5
let votesDoubleAverage: Double = votes.average()   // 5.5

如果您需要使用Decimal类型的总和，那么它已经被AdditiveArithmetic协议扩展方法所涵盖，因此您只需要实现平均值：

extension Collection where Element == Decimal {
    func average() -> Decimal { isEmpty ? .zero : sum() / Decimal(count) }
}

如果您需要对自定义结构的某个属性求和，我们可以扩展Sequence并创建一个以KeyPath作为参数来计算其总和的方法：

extension Sequence  {
    func sum<T: AdditiveArithmetic>(_ keyPath: KeyPath<Element, T>) -> T {
        reduce(.zero) { $0 + $1[keyPath: keyPath] }
    }
}

用法：

let users: [User] = [
    .init(name: "Steve", age: 45),
    .init(name: "Tim", age: 50)]

let ageSum = users.sum(\.age) // 95

并扩展集合以计算其平均值：

extension Collection {
    func average<I: BinaryInteger>(_ keyPath: KeyPath<Element, I>) -> I {
        sum(keyPath) / I(count)
    }
    func average<I: BinaryInteger, F: BinaryFloatingPoint>(_ keyPath: KeyPath<Element, I>) -> F {
        F(sum(keyPath)) / F(count)
    }
    func average<F: BinaryFloatingPoint>(_ keyPath: KeyPath<Element, F>) -> F {
        sum(keyPath) / F(count)
    }
    func average(_ keyPath: KeyPath<Element, Decimal>) -> Decimal {
        sum(keyPath) / Decimal(count)
    }
}

用法：

let ageAvg = users.average(\.age)                 // 47
let ageAvgDouble: Double = users.average(\.age)   // 47.5