Is there a way to get the difference between two sets of objects in c#

Question

I want to get the difference between two sets of ints in c#. Given s1 and s2 I want to return those ints which are in s1 and not in s2. I can do something such as:

    List<int> s1 = new List<int>();
    List<int> s2 = new List<int>();

    foreach (int i in s1)
    {
        if (s1.Contains(i))
        {
            //
        }
        else
        {
            //
        }
    }

But I was wondering if anyone can point out anything cleaner. I would like to do something such as

List<int> omitted = s1.Difference(s2);

Not sure if there is an existing method or a LINQ construct that anyone might be able to point out? Thank you.

Answer 1

I think you want HashSet.Except. That is, rather than use Lists, use HashSets, and then the operation is available. This is a better type if what you are representing is really a 'set' anyway. (If you already have a list, you can just create a 'new HashSet' out of it.)

Answer 2

from x in s1
where ! s2.contains(x)
select x

Answer 3

List<int> s1 = new List<int>();
List<int> s2 = new List<int>();

return sl.FindAll( i => !s2.Contains(i) )

Answer 4

IEnumerable<T> a, b;

var added = a.Except(b);
var removed = b.Except(a);