[Summary view]

   1  <?php
   2  
   3  declare(strict_types=1);
   4  
   5  namespace Phpml\Classification;
   6  
   7  use Phpml\Helper\Predictable;
   8  use Phpml\Helper\Trainable;
   9  use Phpml\Math\Distance;
  10  use Phpml\Math\Distance\Euclidean;
  11  
  12  class KNearestNeighbors implements Classifier
  13  {
  14      use Trainable;
  15      use Predictable;
  16  
  17      /**
  18       * @var int
  19       */
  20      private $k;
  21  
  22      /**
  23       * @var Distance
  24       */
  25      private $distanceMetric;
  26  
  27      /**
  28       * @param Distance|null $distanceMetric (if null then Euclidean distance as default)
  29       */
  30      public function __construct(int $k = 3, ?Distance $distanceMetric = null)
  31      {
  32          if ($distanceMetric === null) {
  33              $distanceMetric = new Euclidean();
  34          }
  35  
  36          $this->k = $k;
  37          $this->samples = [];
  38          $this->targets = [];
  39          $this->distanceMetric = $distanceMetric;
  40      }
  41  
  42      /**
  43       * @return mixed
  44       */
  45      protected function predictSample(array $sample)
  46      {
  47          $distances = $this->kNeighborsDistances($sample);
  48          $predictions = (array) array_combine(array_values($this->targets), array_fill(0, count($this->targets), 0));
  49  
  50          foreach (array_keys($distances) as $index) {
  51              ++$predictions[$this->targets[$index]];
  52          }
  53  
  54          arsort($predictions);
  55          reset($predictions);
  56  
  57          return key($predictions);
  58      }
  59  
  60      /**
  61       * @throws \Phpml\Exception\InvalidArgumentException
  62       */
  63      private function kNeighborsDistances(array $sample): array
  64      {
  65          $distances = [];
  66  
  67          foreach ($this->samples as $index => $neighbor) {
  68              $distances[$index] = $this->distanceMetric->distance($sample, $neighbor);
  69          }
  70  
  71          asort($distances);
  72  
  73          return array_slice($distances, 0, $this->k, true);
  74      }
  75  }