Ranker

A Ruby library for ranking scorable types using various ranking strategies.

Compatibility

Ranker is tested against MRI (1.8.7+) and JRuby (1.9.0+).

Installation

With bundler, add the ranker gem to your Gemfile.

gem "ranker"

Require the ranker gem in your application.

require "ranker"

Usage

Default Ranking

Default ranking will assume values are numeric and rank them in their natural sorting (ascending) order. For example, a score of 100 is higher than a score of 50.

scores = [1, 1, 2, 3, 3, 1, 4, 4, 5, 6, 8, 1, 0, 8]

rankings = Ranker.rank(scores)
rankings.count #=> 8

ranking = rankings[0]
ranking.rank #=> 1
ranking.score #=> 8
ranking.rankables #=> [8, 8]
ranking.percentile #=> 100
ranking.z_score #=> 1.83921346366645

Custom Ranking

Custom ranking allows for ranking of objects by using a symbol or a lambda.

class Player
  attr_accesor :score

  def initalize(score)
    @score = score
  end
end

players = [Player.new(0), Player.new(100), Player.new(1000), Player.new(25)]
rankings = Ranker.rank(players, :by => lambda { |player| player.score })
# or
rankings = Ranker.rank(players, :by => :score)

In some cases objects need to be ranked by score in descending order, for example, if you were ranking golf players. In this case a score of 75 is higher than a score of 100.

class GolfPlayer < Player
end

players = [GolfPlayer.new(72), GolfPlayer.new(100), GolfPlayer.new(138), GolfPlayer.new(54)]
rankings = Ranker.rank(players, :by => :score, :asc => false)

Ranking Strategies

Ranker has a number of ranking strategies available to use, mostly based on the Wikipedia entry on ranking. Strategies can be passed in as an option to the rank method.

rankings = Ranker.rank(players, :by => :score, :strategy => :ordinal)

Standard Competition Ranking ("1224" ranking)

This is the default ranking strategy. For more info, see the Wikipedia entry on Standard Competition Ranking.

rankings = Ranker.rank(players, :by => :score, :strategy => :standard_competition)

Modified Competition Ranking ("1334" ranking)

For more info, see the Wikipedia entry on Modified Competition Ranking.

rankings = Ranker.rank(players, :by => :score, :strategy => :modified_competition)

Dense Ranking ("1223" ranking)

For more info, see the Wikipedia entry on Dense Ranking.

rankings = Ranker.rank(players, :by => :score, :strategy => :dense)

Ordinal Ranking ("1234" ranking)

For more info, see the Wikipedia entry on Ordinal Ranking.

rankings = Ranker.rank(players, :by => :score, :strategy => :ordinal)

Custom Ranking

If you find the current strategies not to your liking, you can write your own and pass the class into the rank method.

class MyCustomStrategy < Ranker::Strategies::Strategy

  def execute
    # My code here
  end

end

rankings = Ranker.rank(players, :by => :score, :strategy => MyCustomStrategy)

Copyright

Copyright © 2013 Ilya Scharrenbroich. Released under the MIT License.