LINQ GroupBy by several values with IComparable exception

Question

I have list with possible values

|Team| |Year| Wins| "Team1" 2014 7 "Team2" 2015 9 "Team1" 2014 8

I wanna get result as

|Team| |Year| Wins| "Team1" 2014 15 "Team2" 2015 9

I try to do that but I get At least one one object must implement Icomparable

 gameResults =
                    gameResults.GroupBy(t => new{t.ContendersName, t.Year})
                    .OrderBy(g => g.Key)
                    .Select(g => new PivotTeamResult()
                       {
                           ContendersName = g.Key.ContendersName,
                           Year = g.Key.Year,
                           Wins = g.Sum(x => x.Wins)                          

                       }).ToList();

I implement IComparable as

public int CompareTo(object obj) {

        PivotTeamResult teamResult = (PivotTeamResult)obj;

        if (this.ContendersName == teamResult.ContendersName)
        {
              return this.Year.CompareTo(teamResult.Year);
        }

        return teamResult.ContendersName.CompareTo(this.ContendersName);
    }

How I can get right result?

Answer 1

I'm not sure but i think your problem lies in OrderBy and not the GroupBy statement. As i see it, you are trying to OrderBy a group key which is not comparable and can't be sorted.

Maybe this will work:

  gameResults =
                gameResults.GroupBy(t => new{t.ContendersName, t.Year})
                .OrderBy(g => g.Key.ContendersName)
                .Select(g => new PivotTeamResult()
                   {
                       ContendersName = g.Key.ContendersName,
                       Year = g.Key.Year,
                       Wins = g.Sum(x => x.Wins)                          

                   }).ToList();

Answer 2

Here you have implemented a comparer for the PivotTeamResult but in the OrderBy clause you are comparing the anonymous type {t.ContendersName, t.Year} so you may perform the order directly like :

gameResults =
                gameResults.GroupBy(t => new{t.ContendersName, t.Year})
                .OrderBy(g => g.Key.ContendersName)
                .ThenBy(g => g.Key.Year)
                .Select(g => new PivotTeamResult()
                   {
                       ContendersName = g.Key.ContendersName,
                       Year = g.Key.Year,
                       Wins = g.Sum(x => x.Wins)                          

                   }).ToList();

Answer 3

Your CompareTo method isn't safe enough because of (PivotTeamResult)obj ; I think that's what you need:

gameResults = gameResults.GroupBy(t => new {t.ContendersName, t.Year}).Select(
                   g => new PivotTeamResult()
                   {
                       ContendersName = g.Key.ContendersName,
                       Year = g.Key.Year,
                       Wins = g.Sum(x => x.Wins)                          

                   }).ToList();

IComparable must be implemented if you want to use OrderBy, Sort or other methods which use object's comparison, in this case it isn't neccessary