Remove elements from one List that are found in another

Question

I have two lists

 List list1 = new List();
 List list2 = new List();

I want remove all elements from li

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