naive statistics playground for kid's homework.

stats.swift

import Foundation

func mean(_ values: [Float]) -> Float {
    return sum(values) / Float(values.count)
}

func median(_ values: [Float]) -> Float {
    var sorted = values.sorted()
    guard values.count > 0 else { return 0 }
    while sorted.count > 2 {
        sorted.popLast()
        sorted.removeFirst()
    }
    return mean(sorted)
}

func sum(_ values: [Float]) -> Float {
    var a: Float = 0
    for i in values {
        a = a + i
    }
    return a
}

func mode(_ values: [Float]) -> Float {
    var counts: [Float: Int] = [:]
    for i in values {
        counts[i, default: 0] += 1
    }
    guard values.count > 0 else { return 0 }
    let pairs = Array(counts.enumerated()).map{$0.element}
    print(pairs)
    return pairs.sorted { lhs, rhs in
        return lhs.value < rhs.value
    }.last!.key
}

func popStdDev(_ values: [Float]) -> Float {
    let m = mean(values)
    var sumOfSquaredDiffs: Float = 0
    for i in values {
        let diff = i - m
        sumOfSquaredDiffs += diff * diff
    }
    return sqrtf(sumOfSquaredDiffs / Float(values.count))
}

let births: [Float] = [1,2,2,2,2,2,2,2,2,3,3,3,4,4,4]

median(births)
mean(births)
mode(births)
popStdDev(births)