LINQ Ring: Any() vs Contains() for Huge Collections

Question

Given a huge collection of objects, is there a performance difference between the the following?

Collection.Contains:

myCollection.Contains(myElement) 

Enumerable.Any:

myCollection.Any(currentElement => currentElement == myElement) 

Answer 1

Contains() is an instance method, and its performance depends largely on the collection itself. For instance, Contains() on a List is O(n), while Contains() on a HashSet is O(1).

Any() is an extension method, and will simply go through the collection, applying the delegate on every object. It therefore has a complexity of O(n).

Any() is more flexible however since you can pass a delegate. Contains() can only accept an object.

Answer 2

It depends on the collection. If you have an ordered collection, then Contains might do a smart search (binary, hash, b-tree, etc.), while with `Any() you are basically stuck with enumerating until you find it (assuming LINQ-to-Objects).

Also note that in your example, Any() is using the == operator which will check for referential equality, while Contains will use IEquatable<T> or the Equals() method, which might be overridden.