Difference between two lists

Question

I Have two generic list filled with CustomsObjects.

I need to retrieve the difference between those two lists(Items who are in the first without the items in the sec

Answer 1

Since the Except extension method operates on two IEumerables, it seems to me that it will be a O(n^2) operation. If performance is an issue (if say your lists are large), I'd suggest creating a HashSet from list1 and use HashSet's ExceptWith method.