MathFunctions.swift

//
// Created by Roland Kakonyi on 2018. 01. 29.
// Based on https://github.com/edekhayser/Tweeting-in-Swift
//

import Foundation

/**Arithmetic Mean

:param: array The array that the arithmetic mean will be found for.
:returns: The arithmetic mean of the input array.
*/
func aMean(_ array: [Double]) -> Double {
    return array.reduce(0.0, +) / Double(array.count)
}

/**Geometric Mean

:param: array The array that the geometric mean will be found for.
:returns: The geometric mean of the input array.
*/
func gMean(_ array: [Double]) -> Double {
    return pow(array.reduce(1.0, *), 1.0 / Double(array.count))
}

/**Median

:param: array The array that the median will be found for.
:returns: The median of the input array.
*/
func med(_ array: [Double]) -> Double {
    var sorted = array.sorted(by: <)
    let l = sorted.count
    return l % 2 == 0 ? (sorted[l / 2] + sorted[l / 2 + 1]) / 2 : sorted[l / 2]
}

/**Standard Deviation (Population)

:param: array The array that the population standard deviation will be found for.
:returns: The population standard deviation of the input array.
*/
func stdDevPop(_ array: [Double]) -> Double {
    let mean = aMean(array)
    return pow(aMean(array.map {
        pow(($0 - mean), 2)
    }), 0.5)
}

/**Standard Deviation (Sample)

:param: array The array that the sample standard deviation will be found for.
:returns: The sample standard deviation of the input array.
*/
func stdDevSample(_ array: [Double]) -> Double {
    let mean = aMean(array)
    return pow(array.map {
        pow(($0 - mean), 2)
    }.reduce(0.0, +) / Double(array.count - 1), 0.5)
}