using System;

using System.Collections.Generic;

using System.Linq;

public class Program

{

    public static void Main()

    {

        var ys = new List<double[]>{new double[]{1, 2, 3, 4, 5}, new double[]{10, 20, 30, 40, 50}, new double[]{100, 200, 300, 400, 500}};

        var res = ys.Pivot().Select(StDev);

        foreach(var val in res){

            Console.WriteLine(val);

        }

    }

    public static double StDev(double[] input)

    {

        double avg = input.Average();

        double sum = input.Select(x => (avg - x) * (avg - x)).Sum();

​

        return Math.Sqrt(sum / input.Length);

    }

}

​

public static class Extensions

{

    public static IEnumerable<T[]> Pivot<T>(this List<T[]> items)

    {

        return items.SelectMany( arr => arr.Select( (x,i) => new{Value=x,Index = i}) )

                    .GroupBy(x => x.Index)

                    .Select(g => g.Select(x => x.Value).ToArray());

    }

}