How to remove duplicate object in List with double key

Question

I have list object's. But it has duplicate records for 2 key - itemId and itemTypeId. How do I remove duplicates from the list?

I tried GroupBy - but it can only use one key at a time.

public class TestObject
{
        public string Name;
        public int itemTypeId;
        public int itemId;
        public int id;
}

List <TestObject> testList = new List<TestObject>();

TestObject to1 = new TestObject();
TestObject to2 = new TestObject();
TestObject to3 = new TestObject():

to1.id = 1;
to1.itemId = 252;
to1.itemTypeId = 1;
to1.Name = "to1";

to2.id = 2;
to2.itemId = 252;
to2.itemTypeId = 1;
to2.Name = "to2";

to3.id = 3;
to3.itemId = 252;
to3.itemTypeId = 2;
to3.Name = "to3"

testList.Add(to1);
testList.Add(to2);
testList.Add(to3);

var result = testList.GroupBy(x=>x.itemId).Select(g => 
g.First()).ToList();

Actual Result :

to1 and to3

Answer 1

You can group with multiple fields using the following syntax, grouping will filter out the duplicate entries:

var testListNoDups = testList.GroupBy(x => new {x.itemId, x.itemTypeId})
                                  .Select(x => x.First())
                                  .ToList();

Answer 2

if you want to modify existing testList, you can try RemoveAll:

 HashSet<Tuple<int, int>> keys = new HashSet<Tuple<int, int>>();

 testList.RemoveAll(x => !keys.Add(Tuple.Create(x.itemId, x.itemTypeId)));     

Here we try to add next key to keys and in case of failure (i.e. key exists in keys) we remove the item from testList