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<?php |
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declare(strict_types = 1); |
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namespace drupol\phpartition; |
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use drupol\phpartition\Contract\PartitionItem; |
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use drupol\phpartition\Partition\Partition; |
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use drupol\phpartition\Partitions\Partitions; |
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/** |
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* Class GreedyAlt. |
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*/ |
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class GreedyAlt extends Partitioner |
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{ |
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/** |
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* {@inheritdoc} |
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*/ |
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protected function fillPartitions(Partitions $partitions, Partition $dataset, int $chunks): void |
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{ |
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// Edge case handling. |
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if ($dataset->count() === $chunks) { |
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foreach ($dataset as $key => $item) { |
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$partitions->partition((int) $key)->exchangeArray([$item]); |
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} |
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return; |
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} |
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// Edge case handling. |
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if (0 === $chunks) { |
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throw new \InvalidArgumentException('Chunks must be different from 0.'); |
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} |
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// Greedy needs a dataset sorted DESC. |
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$dataset->uasort( |
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static function (PartitionItem $left, PartitionItem $right) { |
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return $right->getWeight() <=> $left->getWeight(); |
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} |
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); |
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$partitionsArray = []; |
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$best = $dataset->getWeight() / $chunks; |
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for ($p = 1; $p < $chunks; ++$p) { |
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$partition = $this->getPartitionFactory()::create(); |
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while ($partition->getWeight() < $best && 1 < $dataset->count()) { |
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$key = $this->findOptimalItemKey($partition, $dataset, $best); |
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$partition->append($dataset[$key]); |
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unset($dataset[$key]); |
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$dataset->exchangeArray(\array_values($dataset->getArrayCopy())); |
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} |
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$partitionsArray[] = $partition; |
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} |
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$partitionsArray[] = $dataset; |
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foreach ($partitionsArray as $key => $subset) { |
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$partitions->partition($key)->exchangeArray($subset); |
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} |
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} |
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/** |
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* @param \drupol\phpartition\Partition\Partition $partition |
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* @param \drupol\phpartition\Partition\Partition $dataset |
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* @param float $best |
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* |
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* @return null|false|int|string |
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*/ |
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private function findOptimalItemKey(Partition $partition, Partition $dataset, $best) |
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{ |
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$bounds = $dataset->getBounds(); |
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// If the current partition is empty, then use the highest value of the |
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// dataset. |
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if (0 === $partition->count()) { |
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// As the dataset is sorted DESC, return the highest value. |
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return \key($dataset); |
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} |
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// Find which number in the $dataset would be the best fit by checking |
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// which one is closer to the best solution. |
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// Best solution is the sum of the dataset values divided by the number |
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// of chunks we want to have. |
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$partitionWeightMinusBest = $partition->getWeight() - $best; |
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$solutions = \array_map( |
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static function (PartitionItem $item) use ($partitionWeightMinusBest) { |
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return \abs($partitionWeightMinusBest + $item->getWeight()); |
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}, |
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\iterator_to_array($dataset) |
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); |
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\asort($solutions); |
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return \key($solutions); |
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} |
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} |
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drupol /
phpartition
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