using System;

using System.Collections.Generic;

using System.Diagnostics;

using System.Diagnostics.Contracts;

using System.Linq;

using System.Text;

using System.Threading;

​

    public interface IMonoid<T>

    {

        T Empty { get; }

        T Concat(T x, T y);

    }

​

​

 public class SumDecimal : IMonoid<double>

        {

            public double Concat(double x, double y) => x + y;

            public double Empty => 0;

        }

public class Program

{

    public static void Main()

    {

        var bigList = Enumerable.Range(1, 1000000);

​

Func<IEnumerable<int>, Func<int, IEnumerable<IEnumerable<int>>>> slice = list => size =>

{

    var accumulation = new List<IEnumerable<int>>();

    for (int i = 0; i < list.Count(); i += size)

        accumulation.Add(list.Skip(i).Take(size));

    return accumulation;

};

​

  Func<IEnumerable<IEnumerable<int>>, Func<IMonoid<double>, Func<Func<double, double>, double>>>

      mapReduce = list => monoid => map =>

list.Select(chunk =>

    chunk.Select(Convert.ToDouble).Select(map).Aggregate(monoid.Empty, monoid.Concat)

     ).Aggregate(monoid.Empty, monoid.Concat);

​

var chunks = slice(bigList)(10000);

var sum = mapReduce(chunks)(new SumDecimal())(x => x*x*x);

​

​

        Console.WriteLine(sum);

    }

}