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

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

Answer 2

Using LINQ you can do this:

 List1.RemoveAll(i => !List2.Contains(i));

Answer 3

With LINQ:

var result = list1.Except(list2);

Answer 4

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));

Answer 5

var result = list1.Except(list2);

Answer 6

If you want to remove a list of objects (list2) from another list (list1) use:

list1 = list1.Except(list2).ToList()

Remember to use ToList() to convert IEnumerable<T> to List<T>.