RegiRide, a complete Windows Phone application

using System;

namespace RegiRide.Utils
{
    using System.Collections.Generic;
    using System.Collections.ObjectModel;
    using System.Linq;

    public class LongListCollection<T, TKey> : ObservableCollection<LongListItem<T, TKey>> where T : IComparable<T>
    {
        public LongListCollection()
        {
        }

        public LongListCollection(IEnumerable<T> items, Func<T, TKey> keySelector)
        {
            if (items == null)
            {
                throw new ArgumentException("items");
            }

            var groups = new Dictionary<TKey, LongListItem<T, TKey>>();

            foreach (var item in items.OrderBy(x => x))
            {
                var key = keySelector(item);

                if (groups.ContainsKey(key) == false)
                {
                    groups.Add(key, new LongListItem<T, TKey>(key));
                }

                groups[key].Add(item);
            }

            foreach (var value in groups.Values)
            {
                this.Add(value);
            }
        }
    }
}