--- /dev/null
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+Public License instead of this License.
--- /dev/null
+RubyVote: Election Methods Library in Ruby
+===========================================
+
+:Author: Benjamin Mako Hill
+:Copyright: MIT Media Lab and MIT
+:License: GNU GPL
+
+Summary
+--------
+
+**Version:** 0.1
+
+This software includes an set of classes to tally votes and compute
+winners in elections or votes using a series of different
+methods. Currrently these include:
+
+* Plurality or "winner-take-all"
+* Approval
+* Borda
+* Simple Condorcet
+* Condorcet with Cloneproof SSD
+
+More information can be found at the following pages:
+
+* http://en.wikipedia.org/wiki/Plurality_electoral_system
+* http://en.wikipedia.org/wiki/Approval_voting
+* http://en.wikipedia.org/wiki/Borda_count
+* http://en.wikipedia.org/wiki/Condorcet_method
+* http://en.wikipedia.org/wiki/Shulze_method
+
+Writing support for a new module (e.g., instant runnof voting) is a
+fantastic way to to contribute to this module.
+
+This software is prerelease software. I am both a relatively new Ruby
+progreammming and relatively new to election methods. These election
+methods have bugs and may have bugs that skew results. If you are
+understand Ruby and election methods, please do me a favor and audit
+my code.
+
+
+
+How To Use This Library
+-------------------------
+
+Using this library is relatively simple but will differ per election
+methods. In each case, you will need to ``require`` the appropriate
+file for the type of election you will be running and then create a
+new vote object. You should then either pass an array of votes to the
+object upon creation or pass votes in one at at a time.
+
+
+.. Note:: *You* are responsible for ensuring that the votes are in
+ correct form before you hand them to this module. This will
+ not currently check for most types of invalid votes and does
+ not (currently) accept a list of candidates at creation from
+ which it checks all votes. As such, new candidates will be
+ created when seen. If you think this is a meaningful
+ addition to this library, please send a patch. Otherwise,
+ please check for the validity of votes BEFORE you pass them
+ to this election module.
+
+Examples of each type of election currently supported can be seen in
+the test.rb file distributed in this archive.
+
+ElectionVote Objects
+*********************
+
+Each ElectionVote object has the following exposed attributions:
+
+* ElectionVote#votes -- returns a list of votes that have been tallied
+* ElectionVote#candidates -- returns a list of candidates
+
+Additionally, each subclass will create a #results method which will
+return an ElectionResult subclass of the appropriate type.
+
+Currently, you use this module by creating any of the following types
+of vote objects:
+
+Plurality
+^^^^^^^^^^
+
+This is the most simple "winner-take-all" system. The array passed to
+the new vote object should be an array of strings. Each string is
+counted as one vote for a candidate.
+
+Example::
+
+ require 'election'
+ vote_array = [ "A", "B", "B", "A" ]
+ resultobject = PluralityVote.new(vote_array).result
+
+Approval
+^^^^^^^^^
+
+Approval is similar to plurality voting except that users can vote for
+more than one candidate at once naming all of the candidates that they
+approve of.
+
+Example::
+
+ require 'election'
+ vote_array = [ ["A", "B"], ["B", "A"], ["B"] ]
+ resultobject = ApprovalVote.new(vote_array).result
+
+Borda
+^^^^^^
+
+Borda is a positional voting system and, as a result, takes a list of
+ranked candidates and assigns points to each candidates based on their
+order. In Borda, there are *n* candidate and the first candidates is
+assigned *n* - 1 points and each subsequent candidate is assigned one
+less point. The candidate is assigned no points.
+
+Currently, all candidates should be ranked in each ballot.
+
+Example::
+
+ require 'positional'
+ vote_array = [ ["A", "B"], ["B", "A"], ["B", "A"] ]
+ resultobject = BordaVote.new(vote_array).result
+
+Pure Condorcet
+^^^^^^^^^^^^^^^^
+
+Condorcet is a preferential system and, as such, each vote must list
+of ranked preferences from most to least preferred. Currently, all
+candidates must be listed. No ties are allowed on ballots with the
+current implementation.
+
+Example::
+
+ require 'condorcet'
+ vote_array = [ ["A", "B"], ["B", "A"], ["B", "A"] ]
+ resultobject = PureCondorcetVote.new(vote_array).result
+
+Cloneproof Schwartz Sequential Dropping
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+`Cloneproof SSD` is a Condorcet variant with the ability to create
+winners in circular defeats (e.g., A beats B, B beats C, C beats A)
+where this is no clear winner in Condorcet. It is used identically to
+Pure Condorcet.
+
+Example::
+
+ require 'condorcet'
+ vote_array = [ ["A", "B"], ["B", "A"], ["B", "A"] ]
+ resultobject = CloneproofSSDVote.new(vote_array).result
+
+ElectionResult Objects
+***********************
+
+Each election result object will have the following methods:
+
+* #winner? -- return boolean as to the winner or winners of an election
+* #winners -- an array of winners of the election
+* #ranked_candidates -- (where available) a list of ranked candidates
+
+
+License
+--------
+
+This program is free software; you can redistribute it and/or modify
+it under the terms of the GNU General Public License as published by
+the Free Software Foundation; either version 2 of the License, or (at
+your option) any later version.
+
+This program is distributed in the hope that it will be useful, but
+WITHOUT ANY WARRANTY; without even the implied warranty of
+MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
+General Public License for more details.
+
+You should have received a copy of the GNU General Public License
+along with this program; if not, write to the Free Software
+Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
+02110-1301, USA.
+
+Look in the COPYING file for the text of the GNU GPL.
+
+Authors
+--------
+
+Currently, the only contributor to this program is Benjamin Mako Hill
+working at the MIT Media Lab. Please feel free to contribute to this
+module and get your name added here.
+
+For more information about Mako and his programs, you can seee his
+homepage here:
+
+ http://mako.cc
+
+For more information about the MIT Media Lab, you can see its homepage
+here:
+
+ http://www.media.mit.edu
+
--- /dev/null
+# election library -- a ruby library for elections
+# copyright © 2005 MIT Media Lab and Benjamin Mako Hill
+
+# This program is free software; you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation; either version 2 of the License, or
+# (at your option) any later version.
+
+# This program is distributed in the hope that it will be useful, but
+# WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
+# General Public License for more details.
+
+# You should have received a copy of the GNU General Public License
+# along with this program; if not, write to the Free Software
+# Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
+# 02110-1301, USA.
+
+#################################################################
+## ==== condorcet.rb ====
+##
+## This file contains Condorcet election methods. Currently this
+## includes a pure condorcet and a CloneproofSSD implementation
+## modeled after the Python-based Debian project election code and
+## that gives the same results in several tested corner cases.
+#################################################################
+
+##################################################################
+## CondorcetVote Classes and SubClasses
+##
+## The CondorcetVote class is subclassed by the PureCondorcetVote and
+## the CloneproofSSDVote classes but should not be used directly.
+
+require 'election'
+
+class CondorcetVote < ElectionVote
+
+ def tally_vote(vote=nil)
+
+ vote.each_with_index do |winner, index|
+ # only run through this if this *is* preferred to something
+ break if vote.length - 1 == index
+ losers = vote.last( vote.length - index )
+
+ losers.each do |loser|
+ next if winner == loser
+
+ @votes[winner] = Hash.new unless @votes.has_key?(winner)
+ @votes[loser] = Hash.new unless @votes.has_key?(loser)
+
+ if @votes[winner].has_key?(loser)
+ @votes[winner][loser] += 1
+ else
+ @votes[winner][loser] = 1
+ end
+
+ # make sure we have a comparable object
+ @votes[loser][winner] = 0 unless @votes[loser].has_key?( winner )
+
+ @candidates << loser unless @candidates.include?( loser )
+ end
+
+ @candidates << winner unless @candidates.include?( winner )
+ end
+ end
+
+ protected
+ def verify_vote(vote=nil)
+ vote.instance_of?( Array ) and
+ vote == vote.uniq
+ end
+
+end
+
+class PureCondorcetVote < CondorcetVote
+ def result
+ PureCondorcetResult.new( self )
+ end
+end
+
+class CloneproofSSDVote < CondorcetVote
+ def result
+ CloneproofSSDResult.new( self )
+ end
+end
+
+
+##################################################################
+## CondorcetResult Classes and SubClasses
+##
+## The CondorcetResult class is subclassed by the PureCondorcetResult
+## and the CloneproofSSDResult classes but should not be used
+## directly.
+
+class CondorcetResult < ElectionResult
+ def initialize(voteobj=nil)
+ unless voteobj and voteobj.kind_of?( CondorcetVote )
+ raise ArgumentError, "You must pass a CondorcetVote array.", caller
+ end
+ super(voteobj)
+ end
+
+ protected
+ def defeats(candidates=nil, votes=nil)
+ candidates = @election.candidates unless candidates
+ votes = @election.votes unless votes
+
+ defeats = Array.new
+ candidates.each do |candidate|
+ candidates.each do |challenger|
+ next if candidate == challenger
+ if votes[candidate][challenger] > votes[challenger][candidate]
+ defeats << [ candidate, challenger ]
+ end
+ end
+ end
+
+ defeats
+ end
+
+end
+
+class PureCondorcetResult < CondorcetResult
+ def initialize(voteobj=nil)
+ super(voteobj)
+ self.condorcet()
+ end
+
+ protected
+ def condorcet
+ votes = @election.votes
+ candidates = @election.candidates
+
+ victors = Hash.new
+ candidates.each do |candidate|
+ victors[candidate] = Array.new
+ end
+
+ self.defeats.each do |pair|
+ winner, loser = *pair
+ victors[winner] << loser
+ end
+
+ winners = @election.candidates.find_all do |candidate|
+ victors[candidate].length == @election.candidates.length - 1
+ end
+
+ @winners << winners if winners.length == 1
+ end
+end
+
+class CloneproofSSDResult < CondorcetResult
+ def initialize(voteobj=nil)
+ super(voteobj)
+ @winners = self.cpssd()
+ end
+
+ protected
+ def cpssd
+ votes = @election.votes
+ candidates = *@election.candidates
+
+ def in_schwartz_set?(candidate, candidates, transitive_defeats)
+ candidates.each do |challenger|
+ next if candidate == challenger
+
+ if transitive_defeats.include?( [ challenger, candidate ] ) and
+ not transitive_defeats.include?( [ candidate, challenger ] )
+ return false
+ end
+ end
+ return true
+ end
+
+ loop do
+
+ # see the array with the standard defeats
+ transitive_defeats = self.defeats(candidates, votes)
+
+ candidates.each do |cand1|
+ candidates.each do |cand2|
+ candidates.each do |cand3|
+ if transitive_defeats.include?( [ cand2, cand1 ] ) and
+ transitive_defeats.include?( [ cand1, cand3 ] ) and
+ not transitive_defeats.include?( [ cand2, cand3 ] ) and
+ not cand2 == cand3
+ transitive_defeats << [ cand2, cand3 ]
+ end
+ end
+ end
+ end
+
+ schwartz_set = Array.new
+ candidates.each do |candidate|
+ if in_schwartz_set?(candidate, candidates, transitive_defeats)
+ schwartz_set << candidate
+ end
+ end
+
+ candidates = schwartz_set
+
+ # look through the schwartz set now for defeats
+ defeats = self.defeats(candidates, votes)
+
+ # it's a tie or there's only one option
+ break if defeats.length == 0
+
+ def is_weaker_defeat?( pair1, pair2 )
+ votes = @election.votes
+ if votes[pair1[0]][pair1[1]] > votes[pair2[0]][pair2[1]]
+ return true
+ elsif votes[pair1[0]][pair1[1]] == votes[pair2[0]][pair2[1]] and
+ votes[pair1[1]][pair1[0]] > votes[pair2[1]][pair2[0]]
+ return true
+ else
+ false
+ end
+ end
+
+ defeats.sort! do |pair1, pair2|
+ if is_weaker_defeat?( pair1, pair2 )
+ +1
+ elsif is_weaker_defeat?( pair2, pair1 )
+ -1
+ else
+ 0
+ end
+ end
+
+ votes[defeats[0][0]][defeats[0][1]] = 0
+ votes[defeats[0][1]][defeats[0][0]] = 0
+
+ end
+
+ return candidates
+ end
+
+end
--- /dev/null
+# election library -- a ruby library for elections
+# copyright © 2005 MIT Media Lab and Benjamin Mako Hill
+
+# This program is free software; you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation; either version 2 of the License, or
+# (at your option) any later version.
+
+# This program is distributed in the hope that it will be useful, but
+# WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
+# General Public License for more details.
+
+# You should have received a copy of the GNU General Public License
+# along with this program; if not, write to the Free Software
+# Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
+# 02110-1301, USA.
+
+#################################################################
+## ==== election.rb ====
+##
+## This file contains the core ElectionVote and ElectionResults
+## classes and the most common and simple election methods including
+## plurality and approval voting.
+#################################################################
+
+##################################################################
+## ElectionVote Classes and SubClasses
+##
+## There classes are used to store, verify, and "tally" (i.e. count
+## votes for the standard Election superclass and for the most common
+## types of elections.
+
+class ElectionVote
+ attr_reader :votes
+ attr_reader :candidates
+
+ def initialize(votes=nil)
+ @votes = Hash.new unless defined?(@votes)
+ @candidates = Array.new unless defined?(@candidates)
+
+ if votes
+ if votes.instance_of?( Array )
+ votes.each do |vote|
+ self.tally_vote(vote) if self.verify_vote(vote)
+ end
+ else
+ raise ElectionError, "Votes must be in the form of an array.", caller
+ end
+ end
+ end
+
+ protected
+ # by default, this is set to look if the vote is defined. it should
+ # be overridden in each class
+ def verify_vote(vote=nil)
+ vote ? true : false
+ end
+
+ # by default, this does nothing. it must be redefined in any subclass
+ def tally_vote
+ self.verify_vote(vote)
+ end
+end
+
+class PluralityVote < ElectionVote
+ def result
+ PluralityResult.new(self)
+ end
+
+ protected
+ def verify_vote(vote=nil)
+ vote.instance_of?( String )
+ end
+
+ def tally_vote(candidate)
+ if @votes.has_key?(candidate)
+ @votes[candidate] += 1
+ else
+ @votes[candidate] = 1
+ @candidates << candidate
+ end
+ end
+end
+
+class ApprovalVote < PluralityVote
+ def result
+ ApprovalResult.new(self)
+ end
+
+ protected
+ def verify_vote(vote=nil)
+ vote.instance_of?( Array ) and vote.length >= 1
+ end
+
+ def tally_vote(approvals)
+ approvals.each {|candidate| super(candidate)}
+ end
+end
+
+
+##################################################################
+## Election Result Classes
+##
+
+## There classes are used to compute and report the results of an
+## election. In almost all cases, these will be returned by the
+## #results method of a corresponding ElectionVote subclass.
+
+class ElectionResult
+ attr_reader :winners
+
+ def initialize(voteobj=nil)
+ unless voteobj and voteobj.kind_of?( ElectionVote )
+ raise ArgumentError, "You must pass a ElectionVote array.", caller
+ end
+
+ @election = voteobj
+ @winners = Array.new
+ end
+
+ def winner
+ @winners[0] if @winners.length > 0
+ end
+
+ def winner?
+ @winners.length > 0
+ end
+
+end
+
+class PluralityResult < ElectionResult
+ attr_reader :ranked_candidates
+
+ def initialize(voteobj=nil)
+ super(voteobj)
+
+ votes = @election.votes
+ candidates = @election.candidates
+
+ @ranked_candidates = votes.sort do |a, b|
+ b[1] <=> a[1]
+ end.collect {|a| a[0]}
+
+ # winners are anyone who has the same number of votes as the
+ # first person
+ @winners = @ranked_candidates.find_all do |i|
+ votes[i] == votes[@ranked_candidates[0]]
+ end
+ end
+end
+
+# this class is complete because results for approval are computed
+# identically to results from plurality
+class ApprovalResult < PluralityResult
+end
+
+class ElectionError < ArgumentError
+end
+
--- /dev/null
+# election library -- a ruby library for elections
+# copyright © 2005 MIT Media Lab and Benjamin Mako Hill
+
+# This program is free software; you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation; either version 2 of the License, or
+# (at your option) any later version.
+
+# This program is distributed in the hope that it will be useful, but
+# WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
+# General Public License for more details.
+
+# You should have received a copy of the GNU General Public License
+# along with this program; if not, write to the Free Software
+# Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
+# 02110-1301, USA.
+
+#################################################################
+## ==== positional.rb ====
+##
+## This file contains positional election methods. Currently only
+## includes an implementation of the Borda count election method.
+#################################################################
+
+##################################################################
+## BordaVote and BordaResult Classes
+##
+## These classes inherit from and/or are modeled after the classes in
+## election.rb and condorcet.rb
+
+require 'election'
+
+class BordaVote < ElectionVote
+
+ def initialize(votes=nil)
+ @candidates = Array.new
+ votes.each do |vote|
+ @candidates = vote.uniq if vote.uniq.length > candidates.length
+ end
+ super(votes)
+ end
+
+ def tally_vote(vote)
+ points = candidates.length - 1
+ vote.each do |candidate|
+ @votes[candidate] = points
+ points -= 1
+ end
+ end
+
+ def verify_vote(vote=nil)
+ vote.instance_of?( Array ) and
+ vote == vote.uniq
+ end
+
+ def result
+ BordaResult.new(self)
+ end
+end
+
+class BordaResult < ElectionResult
+ def initialize(voteobj=nil)
+ super(voteobj)
+ votes = @election.votes
+
+ @ranked_candidates = votes.sort do |a, b|
+ b[1] <=> a[1]
+ end.collect {|i| i[0]}
+
+ @winners = @ranked_candidates.find_all do |i|
+ votes[i] == votes[@ranked_candidates[0]]
+ end
+ end
+
+end
--- /dev/null
+#!/usr/bin/ruby -I./lib
+
+# election library -- a ruby library for elections
+# copyright © 2005 MIT Media Lab and Benjamin Mako Hill
+
+# This program is free software; you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation; either version 2 of the License, or
+# (at your option) any later version.
+
+# This program is distributed in the hope that it will be useful, but
+# WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
+# General Public License for more details.
+
+# You should have received a copy of the GNU General Public License
+# along with this program; if not, write to the Free Software
+# Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
+# 02110-1301, USA.
+
+require 'election'
+require 'condorcet'
+require 'positional'
+
+def print_winner(result)
+ if not result.winner?
+ puts "There is no winner."
+ elsif result.winners.length == 1
+ puts "The winner is %s" % result.winners[0]
+ else
+ puts "There is a tie between the following candidates: %s" % result.winners.join(", ")
+ end
+end
+
+def condorcet_test1
+ puts "USING CONDORCET..."
+ puts "The winner should be: B"
+
+ vote_array = Array.new
+ 3.times {vote_array << "ABC".split("")}
+ 3.times {vote_array << "CBA".split("")}
+ 2.times {vote_array << "BAC".split("")}
+
+ print_winner( PureCondorcetVote.new(vote_array).result )
+end
+
+def ssd_test1
+ puts "USING CloneProofSSD..."
+ puts "The winner should be: E"
+
+ vote_array = Array.new
+ 5.times {vote_array << "ACBED".split("")}
+ 5.times {vote_array << "ADECB".split("")}
+ 8.times {vote_array << "BEDAC".split("")}
+ 3.times {vote_array << "CABED".split("")}
+ 7.times {vote_array << "CAEBD".split("")}
+ 2.times {vote_array << "CBADE".split("")}
+ 7.times {vote_array << "DCEBA".split("")}
+ 8.times {vote_array << "EBADC".split("")}
+
+ print_winner( CloneproofSSDVote.new(vote_array).result )
+end
+
+def ssd_test2
+ puts "USING CloneProofSSD..."
+ puts "The winner should be: D"
+
+ vote_array = Array.new
+ 5.times {vote_array << "ACBD".split("")}
+ 2.times {vote_array << "ACDB".split("")}
+ 3.times {vote_array << "ADCB".split("")}
+ 4.times {vote_array << "BACD".split("")}
+ 3.times {vote_array << "CBDA".split("")}
+ 3.times {vote_array << "CDBA".split("")}
+ 1.times {vote_array << "DACB".split("")}
+ 5.times {vote_array << "DBAC".split("")}
+ 4.times {vote_array << "DCBA".split("")}
+
+ print_winner( CloneproofSSDVote.new(vote_array).result )
+end
+
+def ssd_test3
+ puts "USING CloneProofSSD..."
+ puts "The winner should be: B(?)"
+
+ vote_array = Array.new
+ 3.times {vote_array << "ABCD".split("")}
+ 2.times {vote_array << "DABC".split("")}
+ 2.times {vote_array << "DBCA".split("")}
+ 2.times {vote_array << "CBDA".split("")}
+
+ print_winner( CloneproofSSDVote.new(vote_array).result )
+end
+
+
+def borda_test1
+ puts "USING BORDA..."
+ puts "The winner should be: B"
+
+ vote_array = Array.new
+ 3.times {vote_array << "ABC".split("")}
+ 3.times {vote_array << "CBA".split("")}
+ 2.times {vote_array << "BAC".split("")}
+
+ print_winner( BordaVote.new(vote_array).result )
+end
+
+def plurality_test1
+ puts "USING PLURALITY..."
+ puts "The winner should be: C"
+
+ vote_array = "ABCABCABCCCBBAAABABABCCCCCCCCCCCCCA".split("")
+
+ print_winner( PluralityVote.new(vote_array).result )
+end
+
+
+def approval_test1
+ puts "USING APPROVAL..."
+ puts "The winner should be: A"
+
+ vote_array = Array.new
+ 10.times {vote_array << "AB".split("")}
+ 10.times {vote_array << "CB".split("")}
+ 11.times {vote_array << "AC".split("")}
+ 5.times {vote_array << "A".split("")}
+
+ print_winner( ApprovalVote.new(vote_array).result )
+end
+
+condorcet_test1()
+ssd_test1()
+ssd_test2()
+ssd_test3()
+borda_test1()
+plurality_test1()
+approval_test1()
+
projects / rubyvote / commitdiff