Apply Standard Competition Rankings to your leaderboard

README.md

Standard Competition Rankings

This class makes it easier to generate a leaderboard that complies with the Standard Competition Ranking system. That is, it takes joint/tied positions into account, and adjusts the positions accordingly.

Take the following list of users and points for example:

User    | Points
1         35
2         35
3         50
4         10
5         35

You might be contented with a leaderboard like this:

User    | Points    | Position
3         50          1
2         35          2
1         35          3
5         35          4
4         10          5

Users 2, 1 and 5 all have the same points, so what makes user 2 come second, and user 5 come fourth? That can't be right!

What you really need is this:

User    | Points    | Position
3         50          1
2         35          2
1         35          2
5         35          2
4         10          5

Which you can do with the code in this gist!

ranking_data = {...} # hash representation of above user/points table

leaderboard = StandardCompetitionRankings.new(ranking_data, :rank_by => :points, :sort_direction => :desc)
better_leaderboard = leaderboard.calculate

If you don't want any sorting applied because you want to roll your own or whatever, set the :sort_direction parameter to nil or false.

After all that, it will append a field called position to your dataset, which contains your now standardised rankings, and return the whole thing. :)

standard_competition_rankings.rb

class StandardCompetitionRankings

  def initialize(data, options = {})
    @data = data
    @options = options.reverse_merge(:rank_by => :points, :sort_direction => :desc)
  end

  def sort_data!
    return if @options[:sort_direction].nil? or @options[:sort_direction] == false

    case @options[:sort_direction]
    when :desc then @data.sort! {|a, b| b[@options[:rank_by]] <=> a[@options[:rank_by]] }
    when :asc  then @data.sort! {|a, b| a[@options[:rank_by]] <=> b[@options[:rank_by]] }
    else raise ArgumentError, "Sort direction can only be :asc or :desc"
    end
  end

  def calculate
    return @rankings if @rankings.present?

    @rankings = []

    sort_data!

    @data.each_with_index do |data, i|
      if i == 0
        data[:position] = 1
      elsif data[@options[:rank_by]] == @data[i-1][@options[:rank_by]]
        data[:position] = @rankings[i-1][:position]
      else
        data[:position] = i + 1
      end
      @rankings[i] = data
    end

    @rankings
  end

end

standard_competition_rankings_spec.rb

require 'spec_helper'

describe StandardCompetitionRankings do

  let!(:sample_data) do
    %w(1000 2000 3000 3000 4000 5000 6000 7000 7000 9000).map {|points| {:points => points} }
  end

  describe '#calculate' do
    it "should produce rankings with correctly calculated tied positions, sorted ascending" do
      scr = Pokerfed::StandardCompetitionRankings.new(sample_data, :rank_by => :points, :sort_direction => :asc)

      rankings = scr.calculate.map {|r| r[:position] }
      rankings.should == [1, 2, 3, 3, 5, 6, 7, 8, 8, 10]
    end

    it "should produce rankings with correctly calculated tied positions, sorted descending" do
      scr = Pokerfed::StandardCompetitionRankings.new(sample_data, :rank_by => :points, :sort_direction => :desc)

      rankings = scr.calculate.map {|r| r[:position] }
      rankings.should == [1, 2, 2, 4, 5, 6, 7, 7, 9, 10]
    end
  end
end

I'm trying to figure out the best way to extend this class a little to assign appropriate "points" based on standings.

For example, let's say I'm ranking 5 things and the positions come out as 1, 1, 3, 3, and 5. And points are assigned by position as 10, 8, 6, 4, 2.

When there's a tie for 1st, the points for 1st and 2nd should be summed and distributed among the ties. In this case, the resulting points would be:

9, 9, 5, 5, 2.

Any thoughts?