stddev.swift

//: Playground - noun: a place where people can play

import UIKit

extension Array where Element: FloatingPoint {
    /// Returns the sum of all elements in the array
    var total: Element {
        return reduce(0, +)
    }
    /// Returns the average of all elements in the array
    var average: Element {
        return isEmpty ? 0 : total / Element(count)
    }
    
    var variance: Element {
        let mean = average
        let variance = map({ ($0 - mean) * ($0 - mean) }).average
        return variance
    }
    
    var standardDeviation: Element {
        let stdDev = sqrt(variance)
        return stdDev
    }
}

let values: [Double] = [1,2,3]
print(values.standardDeviation)