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Long Term Support Release

  • Bug fixes for general core bugs in 3.9.x will end* 10 May 2021 (12 months).
  • Bug fixes for security issues in 3.9.x will end* 8 May 2023 (36 months).
  • PHP version: minimum PHP 7.2.0 Note: minimum PHP version has increased since Moodle 3.8. PHP 7.3.x and 7.4.x are supported too.
<?php

declare(strict_types=1);

namespace Phpml\Classification\Ensemble;

use Phpml\Classification\Classifier;
use Phpml\Classification\DecisionTree;
use Phpml\Exception\InvalidArgumentException;
use Phpml\Helper\Predictable;
use Phpml\Helper\Trainable;
use ReflectionClass;

class Bagging implements Classifier
{
    use Trainable;
    use Predictable;

    /**
     * @var int
     */
    protected $numSamples;

    /**
     * @var int
     */
    protected $featureCount = 0;

    /**
     * @var int
     */
    protected $numClassifier;

    /**
     * @var string
     */
    protected $classifier = DecisionTree::class;

    /**
     * @var array
     */
< protected $classifierOptions = ['depth' => 20];
> protected $classifierOptions = ['maxDepth' => 20];
/** * @var array */ protected $classifiers = []; /** * @var float */ protected $subsetRatio = 0.7; /** * Creates an ensemble classifier with given number of base classifiers * Default number of base classifiers is 50. * The more number of base classifiers, the better performance but at the cost of procesing time */ public function __construct(int $numClassifier = 50) { $this->numClassifier = $numClassifier; } /** * This method determines the ratio of samples used to create the 'bootstrap' subset, * e.g., random samples drawn from the original dataset with replacement (allow repeats), * to train each base classifier. * * @return $this * * @throws InvalidArgumentException */ public function setSubsetRatio(float $ratio) { if ($ratio < 0.1 || $ratio > 1.0) { throw new InvalidArgumentException('Subset ratio should be between 0.1 and 1.0'); } $this->subsetRatio = $ratio; return $this; } /** * This method is used to set the base classifier. Default value is * DecisionTree::class, but any class that implements the <i>Classifier</i> * can be used. <br> * While giving the parameters of the classifier, the values should be * given in the order they are in the constructor of the classifier and parameter * names are neglected. * * @return $this */ public function setClassifer(string $classifier, array $classifierOptions = []) { $this->classifier = $classifier; $this->classifierOptions = $classifierOptions; return $this; } public function train(array $samples, array $targets): void { $this->samples = array_merge($this->samples, $samples); $this->targets = array_merge($this->targets, $targets); $this->featureCount = count($samples[0]); $this->numSamples = count($this->samples); // Init classifiers and train them with bootstrap samples $this->classifiers = $this->initClassifiers(); $index = 0; foreach ($this->classifiers as $classifier) { [$samples, $targets] = $this->getRandomSubset($index); $classifier->train($samples, $targets); ++$index; } } protected function getRandomSubset(int $index): array { $samples = []; $targets = []; srand($index); $bootstrapSize = $this->subsetRatio * $this->numSamples; for ($i = 0; $i < $bootstrapSize; ++$i) { $rand = random_int(0, $this->numSamples - 1); $samples[] = $this->samples[$rand]; $targets[] = $this->targets[$rand]; } return [$samples, $targets]; } protected function initClassifiers(): array { $classifiers = []; for ($i = 0; $i < $this->numClassifier; ++$i) { $ref = new ReflectionClass($this->classifier); /** @var Classifier $obj */ $obj = count($this->classifierOptions) === 0 ? $ref->newInstance() : $ref->newInstanceArgs($this->classifierOptions); $classifiers[] = $this->initSingleClassifier($obj); } return $classifiers; } protected function initSingleClassifier(Classifier $classifier): Classifier { return $classifier; } /** * @return mixed */ protected function predictSample(array $sample) { $predictions = []; foreach ($this->classifiers as $classifier) { /** @var Classifier $classifier */ $predictions[] = $classifier->predict($sample); } $counts = array_count_values($predictions); arsort($counts); reset($counts); return key($counts); } }