using System;

using System.Collections.Generic;

using System.Linq;

​

namespace Example

{

    static class ExtensionMethods

    {

        static public int AsInteger(this string source)

        {

            int result;

            if (int.TryParse(source, out result)) return result;

            return 0;

        }

    }

    class Item

    {

        public string Name { get; set; }

        public string Amount { get; set; }

    }

    public class Program

    {

        static IEnumerable<IEnumerable<Item>> GroupUp(IEnumerable<Item> input)

        {

            var sorted = input.OrderBy( item => int.Parse(item.Amount) ).GetEnumerator();

            int lastValue = int.MinValue;

            var list = new List<Item>();

            while (sorted.MoveNext())

            {

                var current = sorted.Current;

                var currentAmount = int.Parse(current.Amount);

                var gap = currentAmount - lastValue;

                if (gap < 3)

                {

                    list.Add(current);

                }

                else

                {

                    if (list.Count != 0) yield return list;

                    list = new List<Item>();

                    list.Add(current);

                }

                lastValue = currentAmount;

            }

            if (list.Count != 0) yield return list;

        }

        public static void Main()

        {

            var list = new List<Item>

            {

                new Item { Name = "Jeff", Amount = "20" },

                new Item { Name = "Jack", Amount = "10" },

                new Item { Name = "Ben", Amount = "16" },

                new Item { Name = "Kyle", Amount = "12" }

            };

            var groups = GroupUp(list).ToList();

​

            foreach (var g in groups)

            {

                foreach (var item in g)

                {

                    Console.WriteLine("{0} {1}", item.Name, item.Amount);

                }

                Console.WriteLine();

            }

        }

    }

}

​

​