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   1  <?php
   2  
   3  declare(strict_types=1);
   4  
   5  namespace Phpml\Dataset;
   6  
   7  use Phpml\Exception\InvalidArgumentException;
   8  
   9  /**
  10   * MNIST dataset: http://yann.lecun.com/exdb/mnist/
  11   * original mnist dataset reader: https://github.com/AndrewCarterUK/mnist-neural-network-plain-php
  12   */
  13  final class MnistDataset extends ArrayDataset
  14  {
  15      private const MAGIC_IMAGE = 0x00000803;
  16  
  17      private const MAGIC_LABEL = 0x00000801;
  18  
  19      private const IMAGE_ROWS = 28;
  20  
  21      private const IMAGE_COLS = 28;
  22  
  23      public function __construct(string $imagePath, string $labelPath)
  24      {
  25          $this->samples = $this->readImages($imagePath);
  26          $this->targets = $this->readLabels($labelPath);
  27  
  28          if (count($this->samples) !== count($this->targets)) {
  29              throw new InvalidArgumentException('Must have the same number of images and labels');
  30          }
  31      }
  32  
  33      private function readImages(string $imagePath): array
  34      {
  35          $stream = fopen($imagePath, 'rb');
  36  
  37          if ($stream === false) {
  38              throw new InvalidArgumentException('Could not open file: '.$imagePath);
  39          }
  40  
  41          $images = [];
  42  
  43          try {
  44              $header = fread($stream, 16);
  45  
  46              $fields = unpack('Nmagic/Nsize/Nrows/Ncols', (string) $header);
  47  
  48              if ($fields['magic'] !== self::MAGIC_IMAGE) {
  49                  throw new InvalidArgumentException('Invalid magic number: '.$imagePath);
  50              }
  51  
  52              if ($fields['rows'] != self::IMAGE_ROWS) {
  53                  throw new InvalidArgumentException('Invalid number of image rows: '.$imagePath);
  54              }
  55  
  56              if ($fields['cols'] != self::IMAGE_COLS) {
  57                  throw new InvalidArgumentException('Invalid number of image cols: '.$imagePath);
  58              }
  59  
  60              for ($i = 0; $i < $fields['size']; $i++) {
  61                  $imageBytes = fread($stream, $fields['rows'] * $fields['cols']);
  62  
  63                  // Convert to float between 0 and 1
  64                  $images[] = array_map(function ($b) {
  65                      return $b / 255;
  66                  }, array_values(unpack('C*', (string) $imageBytes)));
  67              }
  68          } finally {
  69              fclose($stream);
  70          }
  71  
  72          return $images;
  73      }
  74  
  75      private function readLabels(string $labelPath): array
  76      {
  77          $stream = fopen($labelPath, 'rb');
  78  
  79          if ($stream === false) {
  80              throw new InvalidArgumentException('Could not open file: '.$labelPath);
  81          }
  82  
  83          $labels = [];
  84  
  85          try {
  86              $header = fread($stream, 8);
  87  
  88              $fields = unpack('Nmagic/Nsize', (string) $header);
  89  
  90              if ($fields['magic'] !== self::MAGIC_LABEL) {
  91                  throw new InvalidArgumentException('Invalid magic number: '.$labelPath);
  92              }
  93  
  94              $labels = fread($stream, $fields['size']);
  95          } finally {
  96              fclose($stream);
  97          }
  98  
  99          return array_values(unpack('C*', (string) $labels));
 100      }
 101  }