php-ml/src/Tree/CART.php
2019-05-12 21:27:21 +02:00

177 lines
4.5 KiB
PHP

<?php
declare(strict_types=1);
namespace Phpml\Tree;
use Phpml\Exception\InvalidArgumentException;
use Phpml\Tree\Node\BinaryNode;
use Phpml\Tree\Node\DecisionNode;
use Phpml\Tree\Node\LeafNode;
abstract class CART
{
/**
* @var DecisionNode|null
*/
protected $root;
/**
* @var int
*/
protected $maxDepth;
/**
* @var int
*/
protected $maxLeafSize;
/**
* @var float
*/
protected $minPurityIncrease;
/**
* @var int
*/
protected $featureCount;
public function __construct(int $maxDepth = PHP_INT_MAX, int $maxLeafSize = 3, float $minPurityIncrease = 0.)
{
if ($maxDepth < 1) {
throw new InvalidArgumentException('Max depth must be greater than 0');
}
if ($maxLeafSize < 1) {
throw new InvalidArgumentException('Max leaf size must be greater than 0');
}
if ($minPurityIncrease < 0.) {
throw new InvalidArgumentException('Min purity increase must be equal or greater than 0');
}
$this->maxDepth = $maxDepth;
$this->maxLeafSize = $maxLeafSize;
$this->minPurityIncrease = $minPurityIncrease;
}
public function root(): ?DecisionNode
{
return $this->root;
}
public function height(): int
{
return $this->root !== null ? $this->root->height() : 0;
}
public function balance(): int
{
return $this->root !== null ? $this->root->balance() : 0;
}
public function bare(): bool
{
return $this->root === null;
}
public function grow(array $samples, array $targets): void
{
$this->featureCount = count($samples[0]);
$depth = 1;
$this->root = $this->split($samples, $targets);
$stack = [[$this->root, $depth]];
while ($stack) {
[$current, $depth] = array_pop($stack) ?? [];
[$left, $right] = $current->groups();
$current->cleanup();
$depth++;
if ($left[1] === [] || $right[1] === []) {
$node = $this->terminate(array_merge($left[1], $right[1]));
$current->attachLeft($node);
$current->attachRight($node);
continue 1;
}
if ($depth >= $this->maxDepth) {
$current->attachLeft($this->terminate($left[1]));
$current->attachRight($this->terminate($right[1]));
continue 1;
}
if (count($left[1]) > $this->maxLeafSize) {
$node = $this->split($left[0], $left[1]);
if ($node->purityIncrease() + 1e-8 > $this->minPurityIncrease) {
$current->attachLeft($node);
$stack[] = [$node, $depth];
} else {
$current->attachLeft($this->terminate($left[1]));
}
} else {
$current->attachLeft($this->terminate($left[1]));
}
if (count($right[1]) > $this->maxLeafSize) {
$node = $this->split($right[0], $right[1]);
if ($node->purityIncrease() + 1e-8 > $this->minPurityIncrease) {
$current->attachRight($node);
$stack[] = [$node, $depth];
} else {
$current->attachRight($this->terminate($right[1]));
}
} else {
$current->attachRight($this->terminate($right[1]));
}
}
}
public function search(array $sample): ?BinaryNode
{
$current = $this->root;
while ($current) {
if ($current instanceof DecisionNode) {
$value = $current->value();
if (is_string($value)) {
if ($sample[$current->column()] === $value) {
$current = $current->left();
} else {
$current = $current->right();
}
} else {
if ($sample[$current->column()] < $value) {
$current = $current->left();
} else {
$current = $current->right();
}
}
continue 1;
}
if ($current instanceof LeafNode) {
break 1;
}
}
return $current;
}
abstract protected function split(array $samples, array $targets): DecisionNode;
abstract protected function terminate(array $targets): BinaryNode;
}