我希望我的函数计算 Double 类型数组的平均值。该数组称为“投票”。目前,我有 10 个号码。
当我调用
average function
来获取数组投票的平均值时,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]
这里如何调用平均值才能得到平均值?
您应该使用
reduce
方法对序列元素求和,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 : 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
输入其总和,它已经被 AdditiveArithmetic
协议扩展方法覆盖,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
并创建一个采用 KeyPath 作为参数来计算其总和的方法:
extension Sequence {
func sum<T: AdditiveArithmetic>(_ predicate: (Element) -> T) -> T {
reduce(.zero) { $0 + predicate($1) }
}
}
用途:
struct User {
let name: String
let age: Int
}
let users: [User] = [
.init(name: "Steve", age: 45),
.init(name: "Tim", age: 50)]
let ageSum = users.sum(\.age) // 95
并扩展集合来计算其平均值:
extension Collection {
func average<T: BinaryInteger>(_ predicate: (Element) -> T) -> T {
sum(predicate) / T(count)
}
func average<T: BinaryInteger, F: BinaryFloatingPoint>(_ predicate: (Element) -> T) -> F {
F(sum(predicate)) / F(count)
}
func average<T: BinaryFloatingPoint>(_ predicate: (Element) -> T) -> T {
sum(predicate) / T(count)
}
func average(_ predicate: (Element) -> Decimal) -> Decimal {
sum(predicate) / Decimal(count)
}
}
用途:
let ageAvg = users.average(\.age) // 47
let ageAvgDouble: Double = users.average(\.age) // 47.5
您的代码中有一些错误:
//You have to set the array-type to Double. Because otherwise Swift thinks that you need an Int-array
var votes:[Double] = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
func average(nums: [Double]) -> Double {
var total = 0.0
//use the parameter-array instead of the global variable votes
for vote in nums{
total += Double(vote)
}
let votesTotal = Double(nums.count)
var average = total/votesTotal
return average
}
var theAverage = average(votes)
一个小衬垫,使用 Swift 翻译的老式 Objective-C KVC:
let average = (votes as NSArray).value(forKeyPath: "@avg.floatValue")
您还可以得到总和:
let sum = (votes as NSArray).value(forKeyPath: "@sum.floatValue")
有关这个长期被遗忘的宝石的更多信息:https://developer.apple.com/library/archive/documentation/Cocoa/Conceptual/KeyValueCoding/CollectionOperators.html
如果需要,可以使用过滤器进行简单平均(Swift 4.2):
let items: [Double] = [0,10,15]
func average(nums: [Double]) -> Double {
let sum = nums.reduce((total: 0, elements: 0)) { (sum, item) -> (total: Double, elements: Double) in
var result = sum
if item > 0 { // example for filter
result.total += item
result.elements += 1
}
return result
}
return sum.elements > 0 ? sum.total / sum.elements : 0
}
let theAvarage = average(nums: items)
我在更新函数中创建了一组信号,为了获得移动平均线,我使用此函数计算由移动平均线周期定义的窗口内的平均值。由于我的目标是组装一组包含平均值的新信号,因此我将丢弃原始组中的信号。对于那些想要在更新函数中(例如在 SKScene 中)使用移动平均值的人来说,这是一个很好的解决方案。
func movingAvarage(_ period: Int) -> Double? {
if signalSet.count >= period {
let window = signalSet.suffix(period)
let mean = (window.reduce(0, +)) / Double(period)
signalSet = signalSet.dropLast(period)
return mean
}
return nil
}
对于纯粹优雅的简约,我喜欢:
// 1. Calls #3
func average <T> (_ values: T...) -> T where T: FloatingPoint
{
return sum(values) / T(values.count)
}
当我们这样做时,其他基于
reduce
的不错的操作:
// 2. Unnecessary, but I appreciate variadic params. Also calls #3.
func sum <T> (_ values: T...) -> T where T: FloatingPoint
{
return sum(values)
}
// 3.
func sum <T> (_ values: [T]) -> T where T: FloatingPoint
{
return values.reduce(0, +)
}
来源:Adrian Houdart 的 MathKit,基本没有变化。
我在 Swift 编程语言中找到了以下内容:
下面的示例计算任意长度的数字列表的算术平均值(也称为平均值):
func arithmeticMean(_ numbers: Double...) -> Double { var total: Double = 0 for number in numbers { total += number } return total / Double(numbers.count) } arithmeticMean(1, 2, 3, 4, 5) // returns 3.0, which is the arithmetic mean of these five numbers arithmeticMean(3, 8.25, 18.75) // returns 10.0, which is the arithmetic mean of these three numbers
将这些扩展添加到数组将计算 Int 和 FloatingPoint 值的平均值:
extension Array where Element: BinaryInteger {
var average: Element? {
guard let elementCount = Element(exactly: count) else { return nil }
return reduce(0) { $0 + $1 } / elementCount
}
}
extension Array where Element: FloatingPoint {
var average: Element? {
guard let elementCount = Element(exactly: count) else { return nil }
return reduce(0) { $0 + $1 } / elementCount
}
}