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<?php |
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/* |
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Kemeny-Young 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\Permutation; |
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use Condorcet\Condorcet; |
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use Condorcet\Result; |
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// Kemeny-Young is a Condorcet Algorithm | http://en.wikipedia.org/wiki/Kemeny%E2%80%93Young_method |
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class KemenyYoung extends Method implements MethodInterface |
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{ |
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// Method Name |
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public const METHOD_NAME = ['Kemeny–Young','Kemeny-Young','Kemeny Young','KemenyYoung','Kemeny rule','VoteFair popularity ranking','Maximum Likelihood Method','Median Relation']; |
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// Method Name |
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public const CONFLICT_WARNING_CODE = 42; |
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// Limits |
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/* If you need to put it on 9, You must use ini_set('memory_limit','1024M'); before. The first use will be slower because Kemeny-Young will work without pre-calculated data of Permutations. |
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Do not try to go to 10, it is not viable! */ |
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public static $_maxCandidates = 8; |
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// Cache |
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public static $useCache = true; |
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// Kemeny Young |
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protected $_PossibleRanking; |
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protected $_RankingScore; |
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/////////// PUBLIC /////////// |
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// Get the Kemeny ranking |
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public function getResult () : Result |
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{ |
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// Cache |
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if ( $this->_Result === null ) : |
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$this->calcPossibleRanking(); |
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$this->calcRankingScore(); |
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$this->makeRanking(); |
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$this->conflictInfos(); |
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endif; |
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// Return |
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return $this->_Result; |
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} |
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protected function getStats () : array |
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{ |
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$explicit = []; |
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foreach ($this->_PossibleRanking as $key => $value) : |
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$explicit[$key] = $value; |
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// Human readable |
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foreach ($explicit[$key] as &$candidate_key) : |
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$candidate_key = $this->_selfElection->getCandidateId($candidate_key); |
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endforeach; |
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$explicit[$key]['score'] = $this->_RankingScore[$key]; |
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endforeach; |
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$stats = []; |
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$stats['bestScore'] = max($this->_RankingScore); |
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$stats['rankingScore'] = $explicit; |
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return $stats; |
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} |
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protected function conflictInfos () : void |
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{ |
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$max = max($this->_RankingScore); |
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$conflict = -1; |
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foreach ($this->_RankingScore as $value) : |
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if ($value === $max) : |
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$conflict++; |
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endif; |
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endforeach; |
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if ($conflict > 0) : |
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$this->_Result->addWarning(self::CONFLICT_WARNING_CODE, ($conflict + 1).';'.max($this->_RankingScore) ); |
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endif; |
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} |
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/////////// COMPUTE /////////// |
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//:: Kemeny-Young ALGORITHM. ::// |
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protected function calcPossibleRanking () : void |
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{ |
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$path = __DIR__ . '/KemenyYoung-Data/'.$this->_selfElection->countCandidates().'.data'; |
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// But ... where are the data ?! Okay, old way now... |
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if (!self::$useCache || !file_exists($path)) : |
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$compute = $this->doPossibleRanking( null ); |
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else : |
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$compute = file_get_contents($path); |
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endif; |
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$i = 0; |
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$search = []; |
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$replace = []; |
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foreach ($this->_selfElection->getCandidatesList() as $candidate_id => $candidate_name) : |
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$search[] = 's:'.(($i < 10) ? "2" : "3").':"C'.$i++.'"'; |
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$replace[] = 'i:'.$candidate_id; |
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endforeach; |
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$this->_PossibleRanking = unserialize( str_replace($search, $replace, $compute) ); |
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} |
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protected function doPossibleRanking (?string $path = null) |
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{ |
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$permutation = new Permutation ($this->_selfElection->countCandidates()); |
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if ($path === null) : |
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return $permutation->getResults(true); |
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else : |
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$permutation->writeResults($path); |
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endif; |
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} |
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protected function calcRankingScore () : void |
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{ |
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$this->_RankingScore = []; |
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$pairwise = $this->_selfElection->getPairwise(false); |
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foreach ($this->_PossibleRanking as $keyScore => $ranking) : |
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$this->_RankingScore[$keyScore] = 0; |
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$do = []; |
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foreach ($ranking as $candidateId) : |
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$do[] = $candidateId; |
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foreach ($ranking as $rank => $rankCandidate) : |
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if (!in_array($rankCandidate, $do, true)) : |
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$this->_RankingScore[$keyScore] += $pairwise[$candidateId]['win'][$rankCandidate]; |
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endif; |
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endforeach; |
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endforeach; |
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endforeach; |
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} |
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/* |
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I do not know how in the very unlikely event that several possible classifications have the same highest score. |
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In the current state, one of them is chosen arbitrarily. |
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See issue on Github : https://github.com/julien-boudry/Condorcet/issues/6 |
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*/ |
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protected function makeRanking () : void |
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{ |
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$this->_Result = $this->createResult($this->_PossibleRanking[ array_search(max($this->_RankingScore), $this->_RankingScore, true) ]); |
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} |
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} |
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julien-boudry /
Condorcet
