projects.mako.cc - rubyvote/blob - lib/runoff.rb

   1 require 'election'
   2
   3 class InstantRunoffVote < ElectionVote
   4   def initialize(votes=nil)
   5     @candidates = Array.new
   6     votes.each do |vote|
   7       @candidates = vote.uniq if vote.uniq.length > candidates.length
   8     end
   9     super(votes)
  10     @candidates.each do |candidate|
  11       @votes[candidate] = [0, Hash.new] unless @votes.has_key?(candidate)
  12     end
  13   end
  14
  15   def result
  16     InstantRunoffResult.new(self)
  17   end
  18
  19   protected
  20   def tally_vote(vote)
  21     votecopy = vote.dup
  22     candidate = votecopy.shift
  23     votes[candidate] = [0, Hash.new] unless votes.has_key?(candidate)
  24     votes[candidate][0] += 1
  25     if votes[candidate][1].has_key?(votecopy)
  26       votes[candidate][1][votecopy] += 1
  27     else
  28       votes[candidate][1][votecopy] = 1
  29     end
  30   end
  31
  32   def verify_vote(vote=nil)
  33     vote.instance_of?( Array ) and
  34       vote == vote.uniq
  35   end
  36 end
  37
  38 class InstantRunoffResult < ElectionResult
  39   attr_reader :ranked_candidates
  40
  41   def initialize(voteobj=nil)
  42     unless voteobj and voteobj.kind_of?( InstantRunoffVote )
  43       raise ArgumentError, "You must pass an InstantRunoffVote array.", caller
  44     end
  45     super(voteobj)
  46
  47     votes = @election.votes.clone
  48     candidates = @election.candidates
  49     majority = votes.inject(0) {|n, value| n + value[1][0]}/2 + 1
  50     @ranked_candidates = Array.new()
  51     ranked_candidates = Array.new()
  52
  53     loop do
  54       ranked_candidates = votes.sort do |a, b|
  55         b[1][0] <=> a[1][0]
  56       end.collect {|i| i[0]}
  57       @winners = ranked_candidates.find_all do |i|
  58         votes[i][0] >= majority
  59       end
  60
  61       loser = ranked_candidates[-1]
  62       break if self.winner? or votes[loser][0] == votes[ranked_candidates[-2]][0]
  63
  64       @ranked_candidates.unshift(loser)
  65       runoff(votes, loser)
  66     end
  67     @ranked_candidates.unshift(*ranked_candidates)
  68   end
  69
  70   def runoff(votes, loser)
  71     votes.each_pair do |candidate, morevotes|
  72       hash = morevotes[1]
  73       hash.each_pair do |vote, count|
  74         hash.delete(vote)
  75         vote.delete(loser)
  76         hash[vote] = count
  77       end
  78     end
  79     votes[loser][1].each_pair do |vote, count|
  80       candidate = vote.shift
  81       votes[candidate][0] += count
  82       if votes[candidate][1].has_key?(vote)
  83         votes[candidate][1][vote] += count
  84       else
  85         votes[candidate][1][vote] = count
  86       end
  87     end
  88     votes.delete(loser)
  89   end
  90 end