Question

I want to create a sorted list of users that appear in one datatable “StatsTable”.

I need to get the userID from StatsTable and then use this to find the UserName in another datatable “UserTable”. When I have these I want to make the userID the Key and the UserName the Value in the sorted list.

I managed to get the userID and add it to the sorted list but the userName is coming through as “System.Data.EnumerableRowCollection`1[System.String]”.

What am I doing wrong? Thanks for your help.

    SortedList UserList = new SortedList();

    List<double> listofUserIDs = StatsTable.AsEnumerable()
    .Select(uid => uid.Field<double>("UserID")).ToList<double>();
    foreach (double UID in listofUserIDs)
    {
        string userName = UserTable.AsEnumerable()
            .Where(id => double.Equals(id.Field<double>("UserID"), UID))
        .Select(name => name.Field<string>("First_Name") + " " + name.Field<string>("Last_Name")).ToString();

         UserList[UID] = userName;
    }

Answer 1

You should use Enumerable.Join to link both tables and select what you need. In this case i would use a Tuple<int, string> whereas the int is the UserID(a UserID with decimal places makes no sense, does it?) and the string is the username:

var query = from rStats in StatsTable.AsEnumerable()
            join rUser in UserTable.AsEnumerable()
            on rStats.Field<int>("UserID") equals rUser.Field<int>("UserID")
            select new {
                UserID   = rStats.Field<int>("UserID"), 
                UserName = string.Format("{0} {1}"
                               , rUser.Field<string>("First_Name")
                               , rUser.Field<string>("Last_Name"))
            };

List<Tuple<int, string>> users = query
    .OrderBy(u => u.UserName)
    .Select(u => Tuple.Create(u.UserID, u.UserName))
    .ToList();

You can access a tuple via the Item properties:

foreach(var user in users)
    Console.WriteLine("UserID:{0} UserName:{1}",user.Item1,user.Item2);