using System;

using System.Linq;

using System.Collections.Generic;

​

public class Program

{

    public static void Main(string[] args)

    {

        double[] raw = 

        {

            36.41,

            37.94,

            38.35,

            37.63,

            36.41,

            36.41,

            36.21,

            36.82,

            37.43,

            37.43,

            37.43,

            37.43,

            37.43,

            37.94,

            37.94,

            37.84,

            37.43,

            37.84,

            37.43,

            37.84,

            37.84

        };

​

        var rawAvgList = raw.Chunk(20).Select(chunk => chunk.Average()).ToArray();

​

        Console.WriteLine(string.Join("\n", rawAvgList));

    }

}

​

public static class EnumerableExt

{

    public static IEnumerable<IEnumerable<T>> Chunk<T>(this IEnumerable<T> values, int chunkSize)

    {

        return values

           .Select((v, i) => new { v, groupIndex = i / chunkSize })

           .GroupBy(x => x.groupIndex)

           .Select(g => g.Select(x => x.v));

    }

}