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

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