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<?php |
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declare(strict_types=1); |
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namespace Smoren\ProbabilitySelector; |
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/** |
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* Probability-based selection manager. |
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* |
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* @template T |
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* |
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* @implements \IteratorAggregate<int, T> |
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*/ |
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class ProbabilitySelector implements \IteratorAggregate |
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{ |
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/** |
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* @var array<T> data storage |
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*/ |
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protected array $data = []; |
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/** |
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* @var array<array{float, int}> |
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*/ |
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protected array $probabilities = []; |
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/** |
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* @var float sum of all the weights of data |
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*/ |
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protected float $weightSum = 0; |
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/** |
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* @var int usage counters sum of data |
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*/ |
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protected int $totalUsageCounter = 0; |
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/** |
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* ProbabilitySelector constructor. |
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* |
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* @param array<array{T, float}|array{T, float, int}> $data |
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*/ |
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public function __construct(array $data = []) |
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{ |
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foreach ($data as $item) { |
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if (\count($item) === 2) { |
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$item[] = 0; |
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} |
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/** @var array{T, float, int} $item */ |
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[$datum, $weight, $usageCounter] = $item; |
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$this->addItem($datum, $weight, $usageCounter); |
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} |
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} |
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/** |
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* Adds datum to the select list. |
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* |
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* @param T $datum datum to add |
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* @param float $weight weight of datum |
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* @param int $usageCounter initial usage counter value for datum |
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* |
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* @return $this |
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*/ |
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public function addItem($datum, float $weight, int $usageCounter): self |
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{ |
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if ($weight <= 0) { |
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throw new \InvalidArgumentException('Weight cannot be negative'); |
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} |
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$this->data[] = $datum; |
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$this->probabilities[] = [$weight, $usageCounter]; |
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$this->weightSum += $weight; |
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$this->totalUsageCounter += $usageCounter; |
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return $this; |
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} |
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/** |
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* Chooses and returns datum from select list, marks it used. |
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* |
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* @return T chosen datum |
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* |
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* @throws \LengthException when selectable list is empty |
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*/ |
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public function decide() |
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{ |
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$maxScore = -INF; |
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$maxScoreWeight = -INF; |
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$maxScoreId = null; |
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if (\count($this->probabilities) === 0) { |
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throw new \LengthException('Candidate not found in empty list'); |
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} |
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foreach ($this->probabilities as $id => [$weight, $usageCounter]) { |
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$score = $weight / ($usageCounter + 1); |
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if ($this->areFloatsEqual($score, $maxScore) && $weight > $maxScoreWeight || $score > $maxScore) { |
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$maxScore = $score; |
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$maxScoreWeight = $weight; |
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$maxScoreId = $id; |
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} |
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} |
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/** @var int $maxScoreId */ |
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$this->incrementUsageCounter($maxScoreId); |
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return $this->data[$maxScoreId]; |
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} |
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/** |
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* Returns iterator to get decisions sequence. |
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* |
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* @param int|null $limit |
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* |
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* @return \Generator |
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*/ |
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public function getIterator(?int $limit = null): \Generator |
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{ |
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for ($i = 0; $limit === null || $i < $limit; ++$i) { |
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yield $this->totalUsageCounter => $this->decide(); |
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} |
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} |
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/** |
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* Increments usage counter of datum by its ID. |
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* |
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* @param int $id datum ID |
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* |
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* @return int current value of usage counter |
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*/ |
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protected function incrementUsageCounter(int $id): int |
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{ |
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$this->totalUsageCounter++; |
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return ++$this->probabilities[$id][1]; |
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} |
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/** |
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* Returns true if parameters are equal. |
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* |
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* @param float $lhs |
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* @param float $rhs |
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* |
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* @return bool |
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*/ |
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protected function areFloatsEqual(float $lhs, float $rhs): bool |
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{ |
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return \abs($lhs - $rhs) < PHP_FLOAT_EPSILON; |
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} |
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} |
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Smoren /
probability-selector-php
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