using System;

using System.Collections.Generic;

using System.Linq;

public class Program

{

    public static void Main()

    {

        var allProducts = new Filter[0];

        List<Filter> groupOne = new List<Filter>();

        List<Filter> groupTwo = new List<Filter>();

        List<Filter> groupThree = new List<Filter>();

        List<Filter> groupFour = new List<Filter>();

​

        for (var i = 0; i < allProducts.Length;)

        {

            if (i < allProducts.Length)

            {

                groupOne.Add(allProducts[i]);

            }

            ++i;

            if (i < allProducts.Length)

            {

                groupTwo.Add(allProducts[i]);

            }

            ++i;

            if (i < allProducts.Length)

            {

                groupThree.Add(allProducts[i]);

            }

            ++i;

            if (i < allProducts.Length)

            {

                groupFour.Add(allProducts[i]);

            }

            ++i;

        }

    }

    class Filter {}

}