Adding the rubyvote library to do the actually election-making. The only

[selectricity] / lib / rubyvote / runoff.rb

diff --git a/lib/rubyvote/runoff.rb b/lib/rubyvote/runoff.rb
new file mode 100644 (file)
index 0000000..8a69a4e
--- /dev/null
+++ b/lib/rubyvote/runoff.rb
@@ -0,0 +1,88 @@
+class InstantRunoffVote < ElectionVote
+  def initialize(votes=nil)
+    @candidates = Array.new
+    votes.each do |vote|
+      @candidates = vote.uniq if vote.uniq.length > candidates.length
+    end
+    super(votes)
+    @candidates.each do |candidate|
+      @votes[candidate] = [0, Hash.new] unless @votes.has_key?(candidate)
+    end
+  end
+
+  def result
+    InstantRunoffResult.new(self)
+  end
+  
+  protected
+  def tally_vote(vote)
+    votecopy = vote.dup
+    candidate = votecopy.shift
+    votes[candidate] = [0, Hash.new] unless votes.has_key?(candidate)
+    votes[candidate][0] += 1
+    if votes[candidate][1].has_key?(votecopy)
+      votes[candidate][1][votecopy] += 1
+    else
+      votes[candidate][1][votecopy] = 1
+    end
+  end
+
+  def verify_vote(vote=nil)
+    vote.instance_of?( Array ) and
+      vote == vote.uniq
+  end
+end
+
+class InstantRunoffResult < ElectionResult
+  attr_reader :ranked_candidates
+
+  def initialize(voteobj=nil)
+    unless voteobj and voteobj.kind_of?( InstantRunoffVote )
+      raise ArgumentError, "You must pass an InstantRunoffVote array.", caller
+    end
+    super(voteobj)
+
+    votes = @election.votes.clone
+    candidates = @election.candidates
+    majority = votes.inject(0) {|n, value| n + value[1][0]}/2 + 1
+    @ranked_candidates = Array.new()
+    ranked_candidates = Array.new()
+
+    loop do
+      ranked_candidates = votes.sort do |a, b|
+        b[1][0] <=> a[1][0]
+      end.collect {|i| i[0]}
+      @winners = ranked_candidates.find_all do |i|
+        votes[i][0] >= majority
+      end
+      
+      loser = ranked_candidates[-1]
+      break if self.winner? or votes[loser][0] == votes[ranked_candidates[-2]][0]
+
+      @ranked_candidates.unshift(loser)
+      runoff(votes, loser) 
+    end
+    @ranked_candidates.unshift(*ranked_candidates)
+  end
+
+  def runoff(votes, loser)
+    votes.each_pair do |candidate, morevotes|
+      hash = morevotes[1]
+      hash.each_pair do |vote, count|
+        hash.delete(vote)
+        vote.delete(loser)
+        hash[vote] = count
+      end
+    end
+    votes[loser][1].each_pair do |vote, count|
+      candidate = vote.shift
+      votes[candidate][0] += count
+      if votes[candidate][1].has_key?(vote)
+        votes[candidate][1][vote] += count
+      else
+        votes[candidate][1][vote] = count
+      end
+    end
+    votes.delete(loser)
+  end
+end