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efrain |
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<?php
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declare(strict_types=1);
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namespace Phpml\Dataset;
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use Phpml\Exception\InvalidArgumentException;
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/**
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* MNIST dataset: http://yann.lecun.com/exdb/mnist/
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* original mnist dataset reader: https://github.com/AndrewCarterUK/mnist-neural-network-plain-php
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*/
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final class MnistDataset extends ArrayDataset
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{
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private const MAGIC_IMAGE = 0x00000803;
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private const MAGIC_LABEL = 0x00000801;
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private const IMAGE_ROWS = 28;
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private const IMAGE_COLS = 28;
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public function __construct(string $imagePath, string $labelPath)
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{
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$this->samples = $this->readImages($imagePath);
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$this->targets = $this->readLabels($labelPath);
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if (count($this->samples) !== count($this->targets)) {
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throw new InvalidArgumentException('Must have the same number of images and labels');
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}
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}
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private function readImages(string $imagePath): array
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{
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$stream = fopen($imagePath, 'rb');
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if ($stream === false) {
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throw new InvalidArgumentException('Could not open file: '.$imagePath);
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}
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$images = [];
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try {
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$header = fread($stream, 16);
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$fields = unpack('Nmagic/Nsize/Nrows/Ncols', (string) $header);
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if ($fields['magic'] !== self::MAGIC_IMAGE) {
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throw new InvalidArgumentException('Invalid magic number: '.$imagePath);
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}
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if ($fields['rows'] != self::IMAGE_ROWS) {
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throw new InvalidArgumentException('Invalid number of image rows: '.$imagePath);
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}
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if ($fields['cols'] != self::IMAGE_COLS) {
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throw new InvalidArgumentException('Invalid number of image cols: '.$imagePath);
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}
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for ($i = 0; $i < $fields['size']; $i++) {
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$imageBytes = fread($stream, $fields['rows'] * $fields['cols']);
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// Convert to float between 0 and 1
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$images[] = array_map(function ($b) {
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return $b / 255;
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}, array_values(unpack('C*', (string) $imageBytes)));
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}
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} finally {
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fclose($stream);
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}
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return $images;
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}
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private function readLabels(string $labelPath): array
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{
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$stream = fopen($labelPath, 'rb');
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if ($stream === false) {
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throw new InvalidArgumentException('Could not open file: '.$labelPath);
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}
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$labels = [];
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try {
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$header = fread($stream, 8);
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$fields = unpack('Nmagic/Nsize', (string) $header);
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if ($fields['magic'] !== self::MAGIC_LABEL) {
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throw new InvalidArgumentException('Invalid magic number: '.$labelPath);
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}
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$labels = fread($stream, $fields['size']);
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} finally {
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fclose($stream);
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}
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return array_values(unpack('C*', (string) $labels));
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}
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}
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