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<?php |
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declare(strict_types=1); |
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namespace Phpml\Tree; |
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use Phpml\Exception\InvalidArgumentException; |
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use Phpml\Tree\Node\BinaryNode; |
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use Phpml\Tree\Node\DecisionNode; |
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use Phpml\Tree\Node\LeafNode; |
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abstract class CART |
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{ |
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/** |
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* @var DecisionNode|null |
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*/ |
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protected $root; |
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/** |
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* @var int |
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*/ |
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protected $maxDepth; |
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/** |
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* @var int |
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*/ |
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protected $maxLeafSize; |
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/** |
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* @var float |
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*/ |
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protected $minPurityIncrease; |
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/** |
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* @var int |
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*/ |
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protected $featureCount; |
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public function __construct(int $maxDepth = PHP_INT_MAX, int $maxLeafSize = 3, float $minPurityIncrease = 0.) |
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{ |
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if ($maxDepth < 1) { |
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throw new InvalidArgumentException('Max depth must be greater than 0'); |
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} |
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if ($maxLeafSize < 1) { |
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throw new InvalidArgumentException('Max leaf size must be greater than 0'); |
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} |
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if ($minPurityIncrease < 0.) { |
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throw new InvalidArgumentException('Min purity increase must be equal or greater than 0'); |
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} |
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$this->maxDepth = $maxDepth; |
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$this->maxLeafSize = $maxLeafSize; |
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$this->minPurityIncrease = $minPurityIncrease; |
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} |
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public function root(): ?DecisionNode |
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{ |
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return $this->root; |
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} |
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public function height(): int |
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{ |
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return $this->root !== null ? $this->root->height() : 0; |
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} |
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public function balance(): int |
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{ |
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return $this->root !== null ? $this->root->balance() : 0; |
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} |
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public function bare(): bool |
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{ |
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return $this->root === null; |
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} |
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public function grow(array $samples, array $targets): void |
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{ |
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$this->featureCount = count($samples[0]); |
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$depth = 1; |
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$this->root = $this->split($samples, $targets); |
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$stack = [[$this->root, $depth]]; |
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while ($stack) { |
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[$current, $depth] = array_pop($stack) ?? []; |
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[$left, $right] = $current->groups(); |
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$current->cleanup(); |
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$depth++; |
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if ($left[1] === [] || $right[1] === []) { |
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$node = $this->terminate(array_merge($left[1], $right[1])); |
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$current->attachLeft($node); |
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$current->attachRight($node); |
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continue 1; |
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} |
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if ($depth >= $this->maxDepth) { |
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$current->attachLeft($this->terminate($left[1])); |
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$current->attachRight($this->terminate($right[1])); |
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continue 1; |
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} |
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if (count($left[1]) > $this->maxLeafSize) { |
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$node = $this->split($left[0], $left[1]); |
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if ($node->purityIncrease() + 1e-8 > $this->minPurityIncrease) { |
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$current->attachLeft($node); |
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$stack[] = [$node, $depth]; |
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} else { |
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$current->attachLeft($this->terminate($left[1])); |
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} |
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} else { |
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$current->attachLeft($this->terminate($left[1])); |
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} |
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if (count($right[1]) > $this->maxLeafSize) { |
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$node = $this->split($right[0], $right[1]); |
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if ($node->purityIncrease() + 1e-8 > $this->minPurityIncrease) { |
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$current->attachRight($node); |
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$stack[] = [$node, $depth]; |
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} else { |
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$current->attachRight($this->terminate($right[1])); |
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} |
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} else { |
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$current->attachRight($this->terminate($right[1])); |
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} |
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} |
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} |
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public function search(array $sample): ?BinaryNode |
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{ |
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$current = $this->root; |
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while ($current) { |
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if ($current instanceof DecisionNode) { |
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$value = $current->value(); |
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if (is_string($value)) { |
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if ($sample[$current->column()] === $value) { |
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$current = $current->left(); |
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} else { |
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$current = $current->right(); |
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} |
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} else { |
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if ($sample[$current->column()] < $value) { |
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$current = $current->left(); |
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} else { |
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$current = $current->right(); |
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} |
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} |
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continue 1; |
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} |
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if ($current instanceof LeafNode) { |
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break 1; |
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} |
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} |
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return $current; |
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} |
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abstract protected function split(array $samples, array $targets): DecisionNode; |
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abstract protected function terminate(array $targets): BinaryNode; |
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} |
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php-ai /
php-ml
This check marks implicit conversions of arrays to boolean values in a comparison. While in PHP an empty array is considered to be equal (but not identical) to false, this is not always apparent.
Consider making the comparison explicit by using
empty(..)or! empty(...)instead.