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", "~> 1.0"

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.