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Differences Between: [Versions 401 and 403]

   1  <?php
   2  
   3  declare(strict_types=1);
   4  
   5  namespace Phpml\Classification\Ensemble;
   6  
   7  use Phpml\Classification\Classifier;
   8  use Phpml\Classification\DecisionTree;
   9  use Phpml\Exception\InvalidArgumentException;
  10  use Phpml\Helper\Predictable;
  11  use Phpml\Helper\Trainable;
  12  use ReflectionClass;
  13  
  14  class Bagging implements Classifier
  15  {
  16      use Trainable;
  17      use Predictable;
  18  
  19      /**
  20       * @var int
  21       */
  22      protected $numSamples;
  23  
  24      /**
  25       * @var int
  26       */
  27      protected $featureCount = 0;
  28  
  29      /**
  30       * @var int
  31       */
  32      protected $numClassifier;
  33  
  34      /**
  35       * @var string
  36       */
  37      protected $classifier = DecisionTree::class;
  38  
  39      /**
  40       * @var array
  41       */
  42      protected $classifierOptions = ['depth' => 20];
  43  
  44      /**
  45       * @var array
  46       */
  47      protected $classifiers = [];
  48  
  49      /**
  50       * @var float
  51       */
  52      protected $subsetRatio = 0.7;
  53  
  54      /**
  55       * Creates an ensemble classifier with given number of base classifiers
  56       * Default number of base classifiers is 50.
  57       * The more number of base classifiers, the better performance but at the cost of procesing time
  58       */
  59      public function __construct(int $numClassifier = 50)
  60      {
  61          $this->numClassifier = $numClassifier;
  62      }
  63  
  64      /**
  65       * This method determines the ratio of samples used to create the 'bootstrap' subset,
  66       * e.g., random samples drawn from the original dataset with replacement (allow repeats),
  67       * to train each base classifier.
  68       *
  69       * @return $this
  70       *
  71       * @throws InvalidArgumentException
  72       */
  73      public function setSubsetRatio(float $ratio)
  74      {
  75          if ($ratio < 0.1 || $ratio > 1.0) {
  76              throw new InvalidArgumentException('Subset ratio should be between 0.1 and 1.0');
  77          }
  78  
  79          $this->subsetRatio = $ratio;
  80  
  81          return $this;
  82      }
  83  
  84      /**
  85       * This method is used to set the base classifier. Default value is
  86       * DecisionTree::class, but any class that implements the <i>Classifier</i>
  87       * can be used. <br>
  88       * While giving the parameters of the classifier, the values should be
  89       * given in the order they are in the constructor of the classifier and parameter
  90       * names are neglected.
  91       *
  92       * @return $this
  93       */
  94      public function setClassifer(string $classifier, array $classifierOptions = [])
  95      {
  96          $this->classifier = $classifier;
  97          $this->classifierOptions = $classifierOptions;
  98  
  99          return $this;
 100      }
 101  
 102      public function train(array $samples, array $targets): void
 103      {
 104          $this->samples = array_merge($this->samples, $samples);
 105          $this->targets = array_merge($this->targets, $targets);
 106          $this->featureCount = count($samples[0]);
 107          $this->numSamples = count($this->samples);
 108  
 109          // Init classifiers and train them with bootstrap samples
 110          $this->classifiers = $this->initClassifiers();
 111          $index = 0;
 112          foreach ($this->classifiers as $classifier) {
 113              [$samples, $targets] = $this->getRandomSubset($index);
 114              $classifier->train($samples, $targets);
 115              ++$index;
 116          }
 117      }
 118  
 119      protected function getRandomSubset(int $index): array
 120      {
 121          $samples = [];
 122          $targets = [];
 123          srand($index);
 124          $bootstrapSize = $this->subsetRatio * $this->numSamples;
 125          for ($i = 0; $i < $bootstrapSize; ++$i) {
 126              $rand = random_int(0, $this->numSamples - 1);
 127              $samples[] = $this->samples[$rand];
 128              $targets[] = $this->targets[$rand];
 129          }
 130  
 131          return [$samples, $targets];
 132      }
 133  
 134      protected function initClassifiers(): array
 135      {
 136          $classifiers = [];
 137          for ($i = 0; $i < $this->numClassifier; ++$i) {
 138              $ref = new ReflectionClass($this->classifier);
 139              /** @var Classifier $obj */
 140              $obj = count($this->classifierOptions) === 0 ? $ref->newInstance() : $ref->newInstanceArgs($this->classifierOptions);
 141  
 142              $classifiers[] = $this->initSingleClassifier($obj);
 143          }
 144  
 145          return $classifiers;
 146      }
 147  
 148      protected function initSingleClassifier(Classifier $classifier): Classifier
 149      {
 150          return $classifier;
 151      }
 152  
 153      /**
 154       * @return mixed
 155       */
 156      protected function predictSample(array $sample)
 157      {
 158          $predictions = [];
 159          foreach ($this->classifiers as $classifier) {
 160              /** @var Classifier $classifier */
 161              $predictions[] = $classifier->predict($sample);
 162          }
 163  
 164          $counts = array_count_values($predictions);
 165          arsort($counts);
 166          reset($counts);
 167  
 168          return key($counts);
 169      }
 170  }