.net - Which method performs better: .Any() vs .Count() > 0?

in the System.Linq namespace, we can now extend our IEnumerable's to have theAny() and Count() extension methods.

I was told recently that if i want to check that a collection contains 1 or more items inside it, I should use the .Any() extension method instead of the .Count() > 0 extension method because the .Count() extension method has to iterate through all the items.

Secondly, some collections have a property (not an extension method) that is Count or Length. Would it be better to use those, instead of .Any() or .Count() ?

yea / nae ?

Answer

If you are starting with something that has a .Length or .Count (such as ICollection, IList, List, etc) - then this will be the fastest option, since it doesn't need to go through the GetEnumerator()/MoveNext()/Dispose() sequence required by Any() to check for a non-empty IEnumerable sequence.

For just IEnumerable, then Any() will generally be quicker, as it only has to look at one iteration. However, note that the LINQ-to-Objects implementation of Count() does check for ICollection (using .Count as an optimisation) - so if your underlying data-source is directly a list/collection, there won't be a huge difference. Don't ask me why it doesn't use the non-generic ICollection...

Of course, if you have used LINQ to filter it etc (Where etc), you will have an iterator-block based sequence, and so this ICollection optimisation is useless.

In general with IEnumerable : stick with Any() ;-p