using System;

using System.Linq;

using System.Collections.Generic;

public static class Program

{

    public static void Main()

    {

        var items = new string[] { "a", "b", "c", "d", "e", "f", "g", "h", "i", "j" };

        var groupedItems = items.GroupBy(3).ToList();

        groupedItems.ForEach(x => 

                             {

                                 Console.WriteLine(x.Key);

                                 x.ToList().ForEach(y => Console.WriteLine("    " + y));

                             });

    }

    public static IEnumerable<IGrouping<int, TSource>> GroupBy<TSource>

              (this IEnumerable<TSource> source, int itemsPerGroup)

    {

        return source.Zip(Enumerable.Range(0, source.Count()),

                          (s, r) => new { Group = r / itemsPerGroup, Item = s })

                    .GroupBy(i => i.Group, g => g.Item)

                    .ToList();

    }

}

​

​