Distinct a list with objects by id

Question

I have a program where there is a topic (like a forum), people can react to that topic.

USER:

1. id
2. first name
3. last name

TOPIC:

1. id
2. subject

REACTION:

1. id
2. topic_id
3. content

Code:

List<USER> ListOfAllUsers = new List<USER>();
var AllReactions = from r in db.REACTIONs
                   where r.topic_id == _topic_id
                   select r;

foreach (var itemX in AllReactions)
{
    ListOfAllUsers.Add(itemX.USER);
}

//Distinct the list of duplicates
var ListOfUsers = ListOfAllUsers.Distinct().ToList();

Now, the "distinct" list still has some duplicates, how do I distinct the list based on the user id's? Or maybe there is another better way to do this. Thanks in advance.

Answer 1

You can use GroupBy to achieve that

var ListOfUsers = ListOfAllUsers.GroupBy(x => x.Id)
                                  .Select(g => g.First())
                                  .ToList();