Problem Statement

Write a stateful function, class, generator or co-routine that takes a series of floating point numbers, one at a time, and returns the running standard deviation of the series. The task implementation should use the most natural programming style of those listed for the function in the implementation language; the task must state which is being used. Do not apply Bessel's correction; the returned standard deviation should always be computed as if the sample seen so far is the entire population.

Use this to compute the standard deviation of this demonstration set,

{ 2 , 4 , 4 , 4 , 5 , 5 , 7 , 9 }

{\displaystyle {2,4,4,4,5,5,7,9}}

, which is

2

{\displaystyle 2}

.

Let's start with the solution:

import "./fmt" for Fmt
import "./math" for Nums

var cumStdDev = Fiber.new { |a|
    for (i in 0...a.count) {
        var b = a[0..i]
        System.print("Values  : %(b)")
        Fiber.yield(Nums.popStdDev(b))
    }
}

var a = [2, 4, 4, 4, 5,  5, 7, 9]
while (true) {
    var sd = cumStdDev.call(a)
    if (cumStdDev.isDone) return
    Fmt.print("Std Dev : $10.8f\n", sd)
}