using System;

using System.Collections.Generic;

using System.Linq;

public class Program

{

    public static void Main()

    {

        var values = new double[]{15.8569444444444};

        StdDev(values).Dump();

        StandardDeviation(values).Dump();

    }

    public static double StdDev(IEnumerable<double> values)

    {

        // ref: http://warrenseen.com/blog/2006/03/13/how-to-calculate-standard-deviation/

        double mean = 0.0;

        double sum = 0.0;

        double stdDev = 0.0;

        int n = 0;

        foreach (double val in values)

        {

            n++;

            double delta = val - mean;

            mean += delta / n;

            sum += delta * (val - mean);

        }

        if (1 < n)

            stdDev = Math.Sqrt(sum / (n - 1));

​

        return stdDev;

    }

    public static double StandardDeviation(IEnumerable<double> valueList)

    {

        double M = 0.0;

        double S = 0.0;

        int k = 1;

        foreach (double value in valueList) 

        {

            double tmpM = M;

            M += (value - tmpM) / k;

            S += (value - tmpM) * (value - M);

            k++;

        }

        return Math.Sqrt(S / (k-1));

    }

}