using System;

using System.Linq;

using System.Reactive;

using System.Reactive.Concurrency;

using System.Reactive.Linq;

using System.Threading;

using System.Windows;

public class Program

{

    public static void Main()

    {

        var data = Enumerable.Range(0, 1000).ToArray();//data生成0から1000まで入ってるarray

        Observable.Zip(

            MakeObservable(0, 250, data),

            MakeObservable(250, 500, data),

            MakeObservable(500, 750, data),

            MakeObservable(750, 1000, data)

        ).Subscribe(x =>

        {

            var sum = 0;

            for(var i = 0; i < x.Count; i++)

            {

                sum += x[i];

                Thread.Sleep(1);

            }

            Console.WriteLine(sum);

        });

    }

    private static IObservable<int> MakeObservable(int startIndex, int endIndex, int[] data)

    {

        return Observable.Start(() => 

        {

            var sum = 0;

            for(var i = startIndex; i < endIndex; i++)

            {

                sum += data[i];

                Thread.Sleep(1);

            }

            return sum;

        });

    }

}