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<?php |
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declare(strict_types=1); |
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namespace Phpml\FeatureExtraction; |
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use Phpml\Tokenization\Tokenizer; |
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use Phpml\Transformer; |
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class TokenCountVectorizer implements Transformer |
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{ |
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/** |
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* @var Tokenizer |
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*/ |
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private $tokenizer; |
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/** |
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* @var StopWords|null |
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*/ |
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private $stopWords; |
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/** |
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* @var float |
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*/ |
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private $minDF; |
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/** |
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* @var array |
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*/ |
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private $vocabulary = []; |
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/** |
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* @var array |
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*/ |
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private $frequencies = []; |
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public function __construct(Tokenizer $tokenizer, ?StopWords $stopWords = null, float $minDF = 0.0) |
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{ |
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$this->tokenizer = $tokenizer; |
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$this->stopWords = $stopWords; |
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$this->minDF = $minDF; |
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} |
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public function fit(array $samples, ?array $targets = null): void |
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{ |
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$this->buildVocabulary($samples); |
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} |
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public function transform(array &$samples, ?array &$targets = null): void |
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{ |
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array_walk($samples, function (string &$sample): void { |
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$this->transformSample($sample); |
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}); |
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$this->checkDocumentFrequency($samples); |
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} |
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public function getVocabulary(): array |
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{ |
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return array_flip($this->vocabulary); |
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} |
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private function buildVocabulary(array &$samples): void |
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{ |
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foreach ($samples as $sample) { |
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$tokens = $this->tokenizer->tokenize($sample); |
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foreach ($tokens as $token) { |
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$this->addTokenToVocabulary($token); |
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} |
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} |
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} |
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private function transformSample(string &$sample): void |
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{ |
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$counts = []; |
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$tokens = $this->tokenizer->tokenize($sample); |
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foreach ($tokens as $token) { |
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$index = $this->getTokenIndex($token); |
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if ($index !== false) { |
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$this->updateFrequency($token); |
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if (!isset($counts[$index])) { |
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$counts[$index] = 0; |
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} |
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++$counts[$index]; |
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} |
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} |
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foreach ($this->vocabulary as $index) { |
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if (!isset($counts[$index])) { |
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$counts[$index] = 0; |
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} |
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} |
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ksort($counts); |
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$sample = $counts; |
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} |
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/** |
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* @return int|bool |
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*/ |
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private function getTokenIndex(string $token) |
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{ |
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if ($this->isStopWord($token)) { |
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return false; |
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} |
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return $this->vocabulary[$token] ?? false; |
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} |
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private function addTokenToVocabulary(string $token): void |
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{ |
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if ($this->isStopWord($token)) { |
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return; |
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} |
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if (!isset($this->vocabulary[$token])) { |
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$this->vocabulary[$token] = count($this->vocabulary); |
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} |
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} |
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private function isStopWord(string $token): bool |
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{ |
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return $this->stopWords !== null && $this->stopWords->isStopWord($token); |
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} |
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private function updateFrequency(string $token): void |
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{ |
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if (!isset($this->frequencies[$token])) { |
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$this->frequencies[$token] = 0; |
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} |
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++$this->frequencies[$token]; |
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} |
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private function checkDocumentFrequency(array &$samples): void |
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{ |
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if ($this->minDF > 0) { |
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$beyondMinimum = $this->getBeyondMinimumIndexes(count($samples)); |
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foreach ($samples as &$sample) { |
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$this->resetBeyondMinimum($sample, $beyondMinimum); |
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} |
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} |
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} |
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private function resetBeyondMinimum(array &$sample, array $beyondMinimum): void |
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{ |
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foreach ($beyondMinimum as $index) { |
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$sample[$index] = 0; |
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} |
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} |
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private function getBeyondMinimumIndexes(int $samplesCount): array |
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{ |
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$indexes = []; |
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foreach ($this->frequencies as $token => $frequency) { |
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if (($frequency / $samplesCount) < $this->minDF) { |
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$indexes[] = $this->getTokenIndex((string) $token); |
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} |
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} |
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return $indexes; |
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} |
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} |
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