From 40b0cd07cb046e687ec92151acbe0aea1c1ef4d4 Mon Sep 17 00:00:00 2001
From: Giuseppe Bilotta <giuseppe.bilotta@gmail.com>
Date: Thu, 11 Dec 2008 17:01:02 +0100
Subject: [PATCH] Add script for ELO ranking computation

---
 milivelo.rb | 102 ++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 102 insertions(+)
 create mode 100755 milivelo.rb

diff --git a/milivelo.rb b/milivelo.rb
new file mode 100755
index 0000000..f6ef074
--- /dev/null
+++ b/milivelo.rb
@@ -0,0 +1,102 @@
+#!/usr/bin/ruby
+
+# Author: Giuseppe "Oblomov" Bilotta <giuseppe.bilotta@gmail.com>
+# License: GPLv2
+
+# Quick & dirty script to calculate ELO rankings. See later of input format.
+
+class Rating
+	# customizable
+	BASE_RATING=1500
+
+	# K factor, can be either fixed, or staircased, or some other function
+	def fixedK(score)
+		# customizable
+		16
+	end
+
+	def rangedK(score)
+		# customizable
+		case score
+		when 0..2100
+			32
+		when 2100..2400
+			24
+		else
+			# > 2400
+			16
+		end
+	end
+
+	def funcK(score)
+		# customizable
+		32 - Math.log(2400)
+	end
+
+	# choose the one we want here
+	alias :factor :fixedK
+
+	attr_reader :rating
+	def initialize
+		# the player list is a hash player => rating that defaults to the base rating
+		@rating = Hash.new { |h, k| h[k] = BASE_RATING }
+	end
+
+	def [](k)
+		@rating[k.to_sym]
+	end
+
+
+	def to_s
+		rating.to_a.sort { |a, b| b.last <=> a.last }.map { |a| a.join(': ') }.join("\n")
+	end
+
+	def update(winner, loser, draw=false)
+		diff = rating[loser] - rating[winner]
+		winner_wins = 1.0/(Math.exp(diff/174)+1)
+		loser_wins = 1.0 - winner_wins
+		score = 1.0
+		score -= 0.5 if draw
+		rating[winner] += factor(rating[winner])*(score - winner_wins)
+		rating[loser] += factor(rating[loser])*(1.0 - score - loser_wins)
+	end
+end
+
+# read lines from standard input, skipping lines that start with a has sign (#)
+# each match line is supposed to be in the form:
+# player1 <=> player2
+# where <=> is < if player2 won, > if player1 won, = if the match was a draw.
+# 2, 1, x are also accepted instead of <, > and = respectively.
+# Lines in the form:
+# player1,player2,<=>
+# are accepted too.
+
+# The player names should have no spaces in them, and anything after the name
+# of the second player is ignored
+
+rating = Rating.new
+$stdin.each_line do |line|
+	# strip comments
+	line.sub!(/#.*/,'')
+		# strip whitespace
+		line.strip!
+	next if line.empty?
+	player1, sign, player2, junk = line.split($;,4)
+	unless sign
+		player1, player2, sign = line.split(/\s*,\s*/,3)
+	end
+	case sign
+	when '2', '<'
+		rating.update(player2.intern, player1.intern)
+	when 'x', 'X', '='
+		rating.update(player2.intern, player1.intern, true)
+	when '1', '>'
+		rating.update(player1.intern, player2.intern)
+	else
+		raise "wrong match sign #{sign.inspect}"
+	end
+	puts "%s,%s,%s,%f,%f" % [player1, player2, sign, rating[player1], rating[player2]]
+end
+
+puts
+puts rating.to_s
-- 
2.32.0.93.g670b81a890