Making my function calculate average of array Swift

Question

I want my function to calculate the average of my Double type array. The array is called "votes". For now, I have 10 numbers.

When I call the average function to get the average of the array votes, it doesn't work.

Here's my code:

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] 

How do I call the average here to get the average?

Answer 1

You should use the reduce method to sum your sequence elements as follow:

Xcode Xcode 10.2+ • Swift 5 or later

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

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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) } } 

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

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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 

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If you need to work with Decimal types its total sum it is already covered by the AdditiveArithmetic protocol extension method, so you only need to implement the average:

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

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If you need to sum a certain property of a custom structure we can extend Sequence and create a method that takes a KeyPath as argument to calculate its sum:

extension Sequence  {     func sum<T: AdditiveArithmetic>(_ predicate: (Element) -> T) -> T {         reduce(.zero) { $0 + predicate($1) }     } } 

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Usage:

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 

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And extend collection to calculate its average:

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)     } } 

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Usage:

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

Answer 2

You have some mistakes in your code:

//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)