c# - Remove elements from one List<T> that are found in another

Question

I have two lists

 List<T> list1 = new List<T>();
 List<T> list2 = new List<T>();

I want remove all elements from list1, which also exist in list2. Of course I can loop through the first loop looking for each element in list2, but I am looking for elegant solution.

Thanks!

Answer 1

To change the actual list1 in place, you could use

list1.RemoveAll(item => list2.Contains(item));

You might instead prefer to simply have a query over the lists without modifying either

var result = list1.Except(list2);

LukeH makes a good recommendation in the comments. In the first version, and if list2 is particularly large, it might be worth it to load the list into a HashSet<T> prior to the RemoveAll invocation. If the list is small, don't worry about it. If you are unsure, test both ways and then you will know.

var theSet = new HashSet<YourType>(list2);
list1.RemoveAll(item => theSet.Contains(item));