Linq find differences in two lists

Question

I have two list of members like this:

Before: Peter, Ken, Julia, Tom

After: Peter, Robert, Julia, Tom

As you can see, Ken is is out and Robert is in.

Answer 1

Your question is not completely specified but I assume that you are looking for the differences as sets (that is, ordering does not matter). If so, you want the symmetric difference of the two sets. You can achieve this using Enumerable.Except:

before.Except(after).Union(after.Except(before));