132 lines
3.0 KiB
PHP
132 lines
3.0 KiB
PHP
<?php
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declare(strict_types=1);
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namespace Phpml\Preprocessing;
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use Phpml\Exception\NormalizerException;
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use Phpml\Math\Statistic\Mean;
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use Phpml\Math\Statistic\StandardDeviation;
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class Normalizer implements Preprocessor
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{
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public const NORM_L1 = 1;
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public const NORM_L2 = 2;
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public const NORM_STD = 3;
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/**
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* @var int
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*/
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private $norm;
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/**
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* @var bool
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*/
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private $fitted = false;
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/**
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* @var array
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*/
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private $std = [];
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/**
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* @var array
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*/
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private $mean = [];
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/**
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* @throws NormalizerException
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*/
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public function __construct(int $norm = self::NORM_L2)
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{
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if (!in_array($norm, [self::NORM_L1, self::NORM_L2, self::NORM_STD], true)) {
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throw new NormalizerException('Unknown norm supplied.');
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}
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$this->norm = $norm;
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}
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public function fit(array $samples, ?array $targets = null): void
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{
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if ($this->fitted) {
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return;
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}
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if ($this->norm === self::NORM_STD) {
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$features = range(0, count($samples[0]) - 1);
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foreach ($features as $i) {
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$values = array_column($samples, $i);
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$this->std[$i] = StandardDeviation::population($values);
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$this->mean[$i] = Mean::arithmetic($values);
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}
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}
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$this->fitted = true;
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}
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public function transform(array &$samples, ?array &$targets = null): void
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{
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$methods = [
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self::NORM_L1 => 'normalizeL1',
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self::NORM_L2 => 'normalizeL2',
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self::NORM_STD => 'normalizeSTD',
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];
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$method = $methods[$this->norm];
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$this->fit($samples);
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foreach ($samples as &$sample) {
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$this->{$method}($sample);
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}
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}
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private function normalizeL1(array &$sample): void
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{
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$norm1 = 0;
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foreach ($sample as $feature) {
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$norm1 += abs($feature);
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}
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if ($norm1 == 0) {
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$count = count($sample);
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$sample = array_fill(0, $count, 1.0 / $count);
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} else {
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array_walk($sample, function (&$feature) use ($norm1): void {
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$feature /= $norm1;
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});
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}
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}
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private function normalizeL2(array &$sample): void
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{
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$norm2 = 0;
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foreach ($sample as $feature) {
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$norm2 += $feature * $feature;
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}
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$norm2 **= .5;
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if ($norm2 == 0) {
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$sample = array_fill(0, count($sample), 1);
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} else {
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array_walk($sample, function (&$feature) use ($norm2): void {
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$feature /= $norm2;
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});
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}
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}
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private function normalizeSTD(array &$sample): void
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{
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foreach (array_keys($sample) as $i) {
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if ($this->std[$i] != 0) {
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$sample[$i] = ($sample[$i] - $this->mean[$i]) / $this->std[$i];
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} else {
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// Same value for all samples.
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$sample[$i] = 0;
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}
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}
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}
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}
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