Shuffle Enumeration

EnumerableExtensions.cs

	public static class EnumerableExtensions
	{
		private static readonly Random rng = new Random();

		public static IEnumerable<T> Shuffle<T>(this IEnumerable<T> source)
		{
			if (source == null)
				throw new ArgumentNullException("source");
			if (rng == null)
				throw new ArgumentNullException("rng");

			return source.ShuffleIterator();
		}

		private static IEnumerable<T> ShuffleIterator<T>(this IEnumerable<T> source)
		{
			T[] elements = source.ToArray();
			// Note i > 0 to avoid final pointless iteration
			for (int i = elements.Length - 1; i > 0; i--)
			{
				// Swap element "i" with a random earlier element it (or itself)
				int swapIndex = rng.Next(i + 1);
				yield return elements[swapIndex];
				elements[swapIndex] = elements[i];
			}

			// there is one item remaining that was not returned - we return it now
			yield return elements[0]; 
		}
	}