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<?php |
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/* |
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Dodgson part of the Condorcet PHP Class |
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By Julien Boudry - 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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// DODGSON Quick is an approximation for Dodgson method | https://www.maa.org/sites/default/files/pdf/cmj_ftp/CMJ/September%202010/3%20Articles/6%2009-229%20Ratliff/Dodgson_CMJ_Final.pdf |
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class DodgsonQuick extends Method implements MethodInterface |
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{ |
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// Method Name |
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public const METHOD_NAME = ['Dodgson Quick','DodgsonQuick','Dodgson Quick Winner']; |
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protected $_Stats; |
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public function getResult () : Result |
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{ |
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// Cache |
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if ( $this->_Result !== null ) : |
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return $this->_Result; |
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endif; |
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$this->computeDodgson(); |
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return $this->_Result; |
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} |
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protected function getStats () : array |
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{ |
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$stats = []; |
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foreach ($this->_Stats as $candidateKey => $dodgsonQuickValue) : |
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$stats[(string) $this->_selfElection->getCandidateId($candidateKey)] = $dodgsonQuickValue; |
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endforeach; |
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return $stats; |
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} |
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/////////// COMPUTE /////////// |
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//:: DODGSON ALGORITHM. ::// |
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protected function computeDodgson () : void |
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{ |
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$pairwise = $this->_selfElection->getPairwise(false); |
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$HeadToHead = []; |
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foreach ($pairwise as $candidateId => $CandidateStats) : |
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foreach ($CandidateStats['lose'] as $opponentId => $CandidateLose) : |
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if (($diff = $CandidateLose - $CandidateStats['win'][$opponentId]) >= 0) : |
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$HeadToHead[$candidateId][$opponentId] = $diff; |
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endif; |
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endforeach; |
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endforeach; |
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$dodgsonQuick = []; |
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foreach ($HeadToHead as $candidateId => $CandidateTidemanScores) : |
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$dodgsonQuick[$candidateId] = 0; |
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foreach ($CandidateTidemanScores as $opponentId => $oneTidemanScore) : |
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$dodgsonQuick[$candidateId] += ceil($oneTidemanScore / 2); |
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endforeach; |
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endforeach; |
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asort($dodgsonQuick); |
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$rank = 0; |
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$result = []; |
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if($basicCondorcetWinner = $this->_selfElection->getWinner(null)) : |
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$result[++$rank][] = $this->_selfElection->getCandidateKey($basicCondorcetWinner); |
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endif; |
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$lastDodgsonQuickValue = null; |
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foreach ($dodgsonQuick as $CandidateId => $dodgsonQuickValue) : |
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if($lastDodgsonQuickValue === $dodgsonQuickValue) : |
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$result[$rank][] = $CandidateId; |
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else: |
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$result[++$rank][] = $CandidateId; |
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$lastDodgsonQuickValue = $dodgsonQuickValue; |
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endif; |
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endforeach; |
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$this->_Stats = $dodgsonQuick; |
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$this->_Result = $this->createResult($result); |
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} |
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} |
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julien-boudry /
Condorcet
