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<?php |
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/* |
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Part of INSTANT-RUNOFF method Module - From the original Condorcet PHP |
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Condorcet PHP - Election manager and results calculator. |
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Designed for the Condorcet method. Integrating a large number of algorithms extending Condorcet. Expandable for all types of voting systems. |
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By Julien Boudry and contributors - MIT LICENSE (Please read LICENSE.txt) |
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https://github.com/julien-boudry/Condorcet |
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*/ |
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declare(strict_types=1); |
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namespace Condorcet\Algo\Methods; |
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use Condorcet\Algo\Method; |
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use Condorcet\Algo\MethodInterface; |
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use Condorcet\Algo\Tools\PairwiseStats; |
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use Condorcet\Result; |
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class InstantRunoff extends Method implements MethodInterface |
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{ |
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// Method Name |
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public const METHOD_NAME = ['Instant-runoff', 'InstantRunoff', 'preferential voting', 'ranked-choice voting', 'alternative vote', 'AlternativeVote', 'transferable vote', 'Vote alternatif']; |
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public static $starting = 1; |
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protected $_Stats; |
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protected function getStats(): array |
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{ |
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$stats = []; |
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foreach ($this->_Stats as $oneIterationKey => $oneIterationData) : |
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if (count($oneIterationData) === 1) : |
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break; |
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endif; |
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foreach ($oneIterationData as $candidateKey => $candidateValue) : |
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$stats[$oneIterationKey][(string) $this->_selfElection->getCandidateId($candidateKey)] = $candidateValue; |
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endforeach; |
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endforeach; |
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return $stats; |
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} |
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/////////// COMPUTE /////////// |
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//:: Alternative Vote ALGORITHM. ::// |
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protected function compute (): void |
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{ |
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$candidateCount = $this->_selfElection->countCandidates(); |
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$majority = $this->_selfElection->sumVotesWeight() / 2; |
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$candidateDone = []; |
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$result = []; |
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$CandidatesWinnerCount = 0; |
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$CandidatesLoserCount = 0; |
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$iteration = 0; |
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while (count($candidateDone) < $candidateCount) : |
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$score = $this->makeScore($candidateDone); |
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$maxScore = max($score); |
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$minScore = min($score); |
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$this->_Stats[++$iteration] = $score; |
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if ( $maxScore > $majority ) : |
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foreach ($score as $candidateKey => $candidateScore) : |
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if ($candidateScore !== $maxScore) : |
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continue; |
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else : |
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$candidateDone[] = $candidateKey; |
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$result[++$CandidatesWinnerCount][] = $candidateKey; |
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endif; |
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endforeach; |
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else : |
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$LosersToRegister = []; |
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foreach ($score as $candidateKey => $candidateScore) : |
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if ($candidateScore !== $minScore) : |
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continue; |
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else : |
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$LosersToRegister[] = $candidateKey; |
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endif; |
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endforeach; |
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// Tie Breaking |
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$round = count($LosersToRegister); |
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for ($i = 1 ; $i < $round ; $i++) : // A little silly. But ultimately shorter and simpler. |
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$LosersToRegister = $this->tieBreaking($LosersToRegister); |
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endfor; |
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$CandidatesLoserCount += count($LosersToRegister); |
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$candidateDone = array_merge($candidateDone, $LosersToRegister); |
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$result[$candidateCount - $CandidatesLoserCount + 1] = $LosersToRegister; |
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endif; |
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endwhile; |
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$this->_Result = $this->createResult($result); |
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} |
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protected function makeScore (array $candidateDone): array |
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{ |
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$score = []; |
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foreach ($this->_selfElection->getCandidatesList() as $oneCandidate) : |
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if (!in_array($this->_selfElection->getCandidateKey($oneCandidate), $candidateDone, true)) : |
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$score[$this->_selfElection->getCandidateKey($oneCandidate)] = 0; |
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endif; |
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endforeach; |
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foreach ($this->_selfElection->getVotesManager() as $oneVote) : |
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$weight = ($this->_selfElection->isVoteWeightIsAllowed()) ? $oneVote->getWeight() : 1; |
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for ($i = 0; $i < $weight; $i++) : |
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$oneRanking = $oneVote->getContextualRanking($this->_selfElection); |
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foreach ($oneRanking as $oneRank) : |
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foreach ($oneRank as $oneCandidate) : |
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if (count($oneRank) !== 1) : |
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break; |
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elseif (!in_array($this->_selfElection->getCandidateKey($oneCandidate), $candidateDone, true)) : |
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$score[$this->_selfElection->getCandidateKey(reset($oneRank))] += 1; |
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break 2; |
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endif; |
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endforeach; |
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endforeach; |
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endfor; |
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endforeach; |
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return $score; |
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} |
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protected function tieBreaking (array $candidatesKeys): array |
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{ |
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$pairwise = $this->_selfElection->getPairwise(false); |
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$pairwiseStats = PairwiseStats::PairwiseComparison($pairwise); |
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$tooKeep = []; |
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foreach ($candidatesKeys as $oneCandidateKeyTotest) : |
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$select = true; |
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foreach ($candidatesKeys as $oneChallengerKey) : |
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if ($oneCandidateKeyTotest === $oneChallengerKey) : |
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continue; |
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endif; |
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if ( $pairwise[$oneCandidateKeyTotest]['win'][$oneChallengerKey] > $pairwise[$oneCandidateKeyTotest]['lose'][$oneChallengerKey] || |
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$pairwiseStats[$oneCandidateKeyTotest]['balance'] > $pairwiseStats[$oneChallengerKey]['balance'] || |
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$pairwiseStats[$oneCandidateKeyTotest]['win'] > $pairwiseStats[$oneChallengerKey]['win'] |
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) : |
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$select = false; |
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endif; |
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endforeach; |
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if ($select) : |
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$tooKeep[] = $oneCandidateKeyTotest; |
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endif; |
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endforeach; |
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return $tooKeep; |
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} |
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} |
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julien-boudry /
Condorcet
