LinqCSharpExtensions.linq

void Main()
{
	// Write code to test your extensions here. Press F5 to compile and run.
}

public static class MyExtensions
{
	// Write custom extension methods here. They will be available to all queries.

	public static bool IsNumeric(this string theValue)
	{
		long retNum;
		return long.TryParse(theValue, System.Globalization.NumberStyles.Integer, System.Globalization.NumberFormatInfo.InvariantInfo, out retNum);
	}

}


// You can also define non-static classes, enums, etc.
public static class CollectionExtensions
{
	public static IEnumerable<TSource> DistinctBy<TSource, TKey>(this IEnumerable<TSource> source, Func<TSource, TKey> keySelector)
	{
		HashSet<TKey> seenKeys = new HashSet<TKey>();
		foreach (TSource element in source)
		{
			if (seenKeys.Add(keySelector(element)))
			{
				yield return element;
			}
		}
	}

	//https://stackoverflow.com/questions/127704/algorithm-to-return-all-combinations-of-k-elements-from-n?page=1&tab=votes#tab-top
	public static IEnumerable<IEnumerable<T>> Combinations<T>(this IEnumerable<T> elements)
	{
		return elements.Count() == 0 ? new[] { new T[0] } :
		  elements.SelectMany((e, i) =>
			elements.Skip(i + 1).Combinations(elements.Count() - 1).Select(c => (new[] { e }).Concat(c)));
	}


	//https://stackoverflow.com/questions/127704/algorithm-to-return-all-combinations-of-k-elements-from-n?page=1&tab=votes#tab-top
	public static IEnumerable<IEnumerable<T>> Combinations<T>(this IEnumerable<T> elements, int k)
	{
		return k == 0 ? new[] { new T[0] } :
		  elements.SelectMany((e, i) =>
			elements.Skip(i + 1).Combinations(k - 1).Select(c => (new[] { e }).Concat(c)));
	}
}