C# Ranking of objects, multiple criteria

Question

I am building a plugin for a LAN party website that I wrote that would allow the use of a Round Robin tournament.

All is going well, but I have some questions about the most efficient way to rank over two criteria.

Basically, I would like the following ranking layout:

         Rank  Wins  TotalScore
PersonE  1     5     50
PersonD  2     3.5   37
PersonA  2     3.5   37
PersonC  4     2.5   26
PersonB  5     2.5   24
PersonF  6     0     12

In SQL server, I would use:

SELECT
    [Person],
    RANK() OVER (ORDER BY Wins DESC, TotalScore DESC) [Rank],
    [Wins],
    [TotalScore]

Now, I only have List, Dictionary, and etc. to work with

Specifically:

Dictionary<TournamentTeam, double> wins = new Dictionary<TournamentTeam, double>();
Dictionary<TournamentTeam, double> score = new Dictionary<TournamentTeam, double>();

Is there a way to do this style of ranking with LINQ?

If not, is there an extensible way that would allow me later to take in to account Win-Loss-Draw instead of just wins if I choose to?

Edit:

My adaptation of TheSoftwareJedi's answer:

private class RRWinRecord : IComparable
{
    public int Wins { get; set; }
    public int Losses { get; set; }
    public int Draws { get; set; }
    public double OverallScore { get; set; }
    public double WinRecord
    {
        get
        {
            return this.Wins * 1.0 + this.Draws * 0.5 + this.Losses * 0.0;
        }
    }

    public int CompareTo(object obj) { ... }

    public override bool Equals(object obj) { ... }
    public override int GetHashCode() { ... }
    public static bool operator ==(RRWinRecord lhs, RRWinRecord rhs) { ... }
    public static bool operator !=(RRWinRecord lhs, RRWinRecord rhs) { ... }
    public static bool operator >(RRWinRecord lhs, RRWinRecord rhs) { ... }
    public static bool operator <(RRWinRecord lhs, RRWinRecord rhs) { ... }
    public static bool operator >=(RRWinRecord lhs, RRWinRecord rhs) { ... }
    public static bool operator <=(RRWinRecord lhs, RRWinRecord rhs) { ... }
}

...

    int r = 1, lastRank = 1;
    RRWinRecord lastRecord = null;

    var ranks = from team in records.Keys
                let teamRecord = records[team]
                orderby teamRecord descending
                select new RRRank() { Team = team, Rank = r++, Record = teamRecord };

    foreach (var rank in ranks)
    {
        if (rank.Record != null && lastRecord == rank.Record)
        {
            rank.Rank = lastRank;
        }

        lastRecord = rank.Record;
        lastRank = rank.Rank;

        string scoreDescription = String.Format("{0}-{1}-{2}", rank.Record.Wins, rank.Record.Losses, rank.Record.Draws);
        yield return new TournamentRanking(rank.Team, rank.Rank, scoreDescription);
    }

    yield break;

Answer 1

Assuming you have a List<Result> structure where the Result object has the following parameters...

Pesron     - string
Rank       - int
Wins       - double
TotalScore - int

You could write a custom comparer, and then pass that to List.Sort(Comparison<Result> comparison)

Alternative, you could just make your Result object implement IComparable<Result> and stick this in your class.

        #region IComparable Members

        public int CompareTo(Result obj)
        {
            if (this.Rank.CompareTo(obj.Rank) != 0)
                return this.Rank.CompareTo(obj.Rank);

            if (this.Wins.CompareTo(obj.Wins) != 0)
                return (this.Wins.CompareTo(obj.Wins);

            return (this.TotalScore.CompareTo(obj.TotalScore) ;

        }

        #endregion

Then you can just call List<Result>.Sort();

Answer 2

Ranking isn't too hard. Just mishmash OrderBy and Select implementation patterns together and you can have an easy to use Ranking extension method. Like this:

    public static IEnumerable<U> Rank<T, TKey, U>
    (
      this IEnumerable<T> source,
      Func<T, TKey> keySelector,
      Func<T, int, U> selector
    )
    {
        if (!source.Any())
        {
            yield break;
        }

        int itemCount = 0;
        T[] ordered = source.OrderBy(keySelector).ToArray();
        TKey previous = keySelector(ordered[0]);
        int rank = 1;
        foreach (T t in ordered)
        {
            itemCount += 1;
            TKey current = keySelector(t);
            if (!current.Equals(previous))
            {
                rank = itemCount;
            }
            yield return selector(t, rank);
            previous = current;
        }
    }

Here's some test code

string[] myNames = new string[]
{ "Bob", "Mark", "John", "Jim", "Lisa", "Dave" };
//
var query = myNames.Rank(s => s.Length, (s, r) => new { s, r });
//
foreach (var x in query)
{
  Console.WriteLine("{0} {1}", x.r, x.s);
}

Which yields these results:

1 Bob
1 Jim
3 Mark
3 John
3 Lisa
3 Dave

Answer 3

This should work for a non-dense rank:

static class Program
{

    static IEnumerable<Result> GetResults(Dictionary<TournamentTeam, double> wins, Dictionary<TournamentTeam, double> scores)
    {
        int r = 1;
        double lastWin = -1;
        double lastScore = -1;
        int lastRank = 1;

        foreach (var rank in from name in wins.Keys
                             let score = scores[name]
                             let win = wins[name]
                             orderby win descending, score descending
                             select new Result { Name = name, Rank = r++, Score = score, Win = win })
        {
            if (lastWin == rank.Win && lastScore == rank.Score)
            {
                rank.Rank = lastRank;
            }
            lastWin = rank.Win;
            lastScore = rank.Score;
            lastRank = rank.Rank;
            yield return rank;
        }
    }
}

class Result
{
    public TournamentTeam Name;
    public int Rank;
    public double Score;
    public double Win;
}

Answer 4

I realize I'm late to the party, but I wanted to take a shot anyhow.

Here is a version which uses LINQ exclusively:

private IEnumerable<TeamRank> GetRankings(Dictionary<TournamentTeam, double> wins, Dictionary<TournamentTeam, double> scores)
{
    var overallRank = 1;

    return
        from team in wins.Keys
        group team by new { Wins = wins[team], TotalScore = scores[team] } into rankGroup
        orderby rankGroup.Key.Wins descending, rankGroup.Key.TotalScore descending
        let currentRank = overallRank++
        from team in rankGroup
        select new TeamRank(team, currentRank, rankGroup.Key.Wins, rankGroup.Key.TotalScore);
}

The return type:

public class TeamRank
{
    public TeamRank(TournamentTeam team, int rank, double wins, double totalScore)
    {
        this.Team = team;
        this.Rank = rank;
        this.Wins = wins;
        this.TotalScore = totalScore;
    }

    public TournamentTeam Team { get; private set; }

    public int Rank { get; private set; }

    public double Wins { get; private set; }

    public double TotalScore { get; private set; }
}

Answer 5

This could be a start:

Dictionary<TournamentTeam, double> wins = new Dictionary<TournamentTeam, double>();
Dictionary<TournamentTeam, double> score = new Dictionary<TournamentTeam, double>();
Dictionary<TournamentTeam, int> ranks = new Dictionary<TournamentTeam, int>();

int r = 1;

ranks = (
    from name 
    in wins.Keys 
    orderby wins[name] descending, scores[name] descending
    select new { Name = name, Rank = r++ })
    .ToDictionary(item => item.Name, item => item.Rank);