How the get the mean, median and stdev from list

Question

Is it possible to get the mean, median and stdev result from the list of list. Here is my initial code that needs to compute:

var myList = new List<List<double>>();

myList.Add(new List<double> { 1, 3, 6, 8});
myList.Add(new List<double> { 1, 2, 3, 4});
myList.Add(new List<double> { 1, 4, 8, 12});

And expected result is to get the mean, median, and stdev of first and last index only:

Mean:   1, 8
Median: 1, 8
Stdev:  0, 3.265986324

I tried to loop the list to get the average but not sure if this is the best way:

 foreach(var i in myList )
            {
                Console.WriteLine(i[0].Average());
            }

Any suggestion/comments TIA

I already stuck now. I can get the mean value using the .average function but I think the result is inconsistent sometimes it is correct and sometimes i'ts wrong — Rock n' Roll, Apr 02 '19 at 05:57
it's just a sample only. I put the variable as string coz this just came from the excel value — Rock n' Roll, Apr 02 '19 at 06:03
Can we assume each of the lists is in order (i.e. it will always be `{1,3,6,8}` not `{1,6,8,3}`)? — mjwills, Apr 02 '19 at 06:06
Possible duplicate of [Calculate median in c#](https://stackoverflow.com/questions/4140719/calculate-median-in-c-sharp) — mjwills, Apr 02 '19 at 06:07

score 2 · Accepted Answer · answered Apr 02 '19 at 06:05

This will get you started by showing how to calculate the Average. Note the use of First or Last to get the first / last entry from each of the sub-lists.

using System;
using System.Collections.Generic;
using System.Linq;

namespace ConsoleApp5
{
    class Program
    {
        static void Main(string[] args)
        {
            var myList = new List<List<double>>();

            myList.Add(new List<double> { 1, 3, 6, 8 });
            myList.Add(new List<double> { 1, 2, 3, 4 });
            myList.Add(new List<double> { 1, 4, 8, 12 });

            var averageFirst= myList.Select(z => z.First()).Average();
            var averageLast = myList.Select(z => z.Last()).Average();

            Console.WriteLine(averageFirst);
            Console.WriteLine(averageLast);

            Console.ReadLine();
        }
    }
}

Cool! this one works on me but how about the median and stdev is there a function as well or do I need to write the formula manually? — Rock n' Roll, Apr 02 '19 at 06:14
Ok I got it now by just putting the number of index that I need. cool very appreciated! — Rock n' Roll, Apr 02 '19 at 06:18

score 0 · Answer 2 · edited Dec 14 '19 at 11:18

I'll join forces with @mjwills (first and last)

Which is to say,

var listOfFirstValues = myList.Select(z => z.First()).ToList();
var listOfLastValues = myList.Select(z => z.Last()).ToList();

Mean

var mean = myList.Average();

Median The middle of a sorted list of numbers

public double Median(List<double> numbers)
{
   if (numbers.Count == 0)
      return 0;

   numbers = numbers.OrderBy(n=>n).ToList(); 

   var halfIndex = numbers.Count()/2; 

   if (numbers.Count() % 2 == 0)
     return (numbers[halfIndex] + numbers[halfIndex - 1]) / 2.0;

   return numbers[halfIndex];
}

Standard Deviation a quantity expressing by how much the members of a group differ from the mean value for the group

private double CalculateStdDev(List<double> values)
{  
   if (values.Count == 0)
      return 0;

   var avg = values.Average();  
   var sum = values.Sum(d => Math.Pow(d - avg, 2));   
   return Math.Sqrt(sum / (values.Count()-1));
}

_{Note : Totally untested, and lacking any sanity checks}

How the get the mean, median and stdev from list

2 Answers2