Please stop using Any() for C# Lists and Arrays

When it comes to performance in C#, even small inefficiencies can add up in large codebases. One common example is the use of the LINQ method .Any() on arrays and lists instead of directly checking .Length or .Count. While .Any() improves readability in some contexts, it introduces measurable overhead when used with collections that already expose a count property.

Benchmark Setup

Using BenchmarkDotNet, I compared .Any() with .Length > 0 for a 100-element integer array. The difference was significant.

Method	Mean	Error	StdDev	Allocated
Any	5.5362 ns	1.0495 ns	0.0575 ns	-
Length	0.2413 ns	0.1316 ns	0.0072 ns	-

As shown above, checking .Length is roughly 30 times faster than using .Any() on an array. The reason is simple: .Length is a direct property access, while .Any() adds the overhead of an enumerator.

Benchmark with Lists

The same comparison was performed using a List<int>. The results are even more striking.

Method	Mean	Error	StdDev	Allocated
Any	2.3934 ns	0.0325 ns	0.0018 ns	-
Count	0.0000 ns	0.0000 ns	0.0000 ns	-

For lists, .Count is effectively instantaneous in this benchmark context - it’s a property access resolved at compile time. In contrast, .Any() must still perform a method call and a single enumerator step.

Why .Any() Is Slower

The LINQ implementation of .Any() does have some optimization routes (if the source list implements ICollection it's smart enough to detect that, but the overhead is still there. And for everything else it simply obtains an enumerator and calls .MoveNext() once to check for the presence of elements. This abstraction introduces a small but measurable overhead compared to directly checking .Count or .Length.

Best Practice

When working with IEnumerable<T> - especially when the underlying type is not known - .Any() remains the correct and idiomatic choice. However, for arrays and lists where you can access .Count or .Length, prefer those properties for both clarity and performance.

In fact, Visual Studio’s code analysis tools will suggest this optimization automatically, recommending direct property checks instead of .Any() when the collection type allows it.