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List<Component> components = new List<Component>
{
    new Component {Region = "One", ComponentId = 1},
    new Component {Region = "One", ComponentId = 2},
    new Component {Region = "Two", ComponentId = 3},
    new Component {Region = "One", ComponentId = 4},
};

regions = components.GroupByAdjacent(c => c.Region)

using System;
using System.Collections;
using System.Collections.Generic;
using System.Linq;

namespace LinqExtensions
{
    internal class Grouping<TElement, TKey> : IEnumerable<TElement>, IGrouping<TKey, TElement>
    {
        private List<TElement> GroupList { get; set; }

        public TKey Key { get; set; }

        IEnumerator IEnumerable.GetEnumerator()
        {
            return ((IEnumerable<TElement>) this).GetEnumerator();
        }

        IEnumerator<TElement> IEnumerable<TElement>.GetEnumerator()
        {
            return ((IEnumerable<TElement>) GroupList).GetEnumerator();
        }

        public Grouping(List<TElement> source, TKey key)
        {
            Key = key;
            GroupList = source;
        }
    }

    public static class LocalExtensions
    {
        public static IEnumerable<IGrouping<TKey, TSource>> GroupByAdjacent<TSource, TKey>(this IEnumerable<TSource> source, Func<TSource, TKey> keySelector)
        {
            if (source == null) throw new ArgumentNullException("source");

            IEnumerator<TSource> enumerator = source.GetEnumerator();
            if (!enumerator.MoveNext()) yield break;

            EqualityComparer<TKey> comparer = EqualityComparer<TKey>.Default;
            List<TSource> elementsSoFar = new List<TSource>();
            TKey lastKey = keySelector(enumerator.Current);

            do
            {
                TKey newKey = keySelector(enumerator.Current);
                if (!comparer.Equals(lastKey, newKey))
                {
                    yield return new Grouping<TSource, TKey>(elementsSoFar, lastKey);
                    lastKey = newKey;
                    elementsSoFar = new List<TSource>();
                }
                elementsSoFar.Add(enumerator.Current);
            } while (enumerator.MoveNext());

            yield return new Grouping<TSource, TKey>(elementsSoFar, lastKey);
        }
    }
}