DataSource Controls :: Count A Row Using LINQ To SQL?

im trying to count the amount of users inside a chatroom, im trying to count a specific row using LINQ to SQL.

Heres the code

DataRowView dataRow = ((DataRowView)e.Item.DataItem);
string roomId = dataRow["RoomID"].ToString();
ChatRoomDataContext db = new ChatRoomDataContext();
var query = from c in db.ChatLoggedInUsers
where c.RoomID.ToString() == roomId.ToString()
select new { };
foreach (var c in query)
{
}

Where " select new { }; " is, is left blank as i am not too sure what goes there. I tried adding c.UserName.Count() but i got an error. what i need to put into that space to count the amount of records in the UserName column?