121 lines
2.9 KiB
PHP
121 lines
2.9 KiB
PHP
<?php
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declare(strict_types=1);
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namespace Phpml\Clustering;
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use Phpml\Math\Distance;
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use Phpml\Math\Distance\Euclidean;
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class DBSCAN implements Clusterer
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{
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private const NOISE = -1;
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/**
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* @var float
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*/
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private $epsilon;
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/**
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* @var int
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*/
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private $minSamples;
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/**
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* @var Distance
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*/
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private $distanceMetric;
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public function __construct(float $epsilon = 0.5, int $minSamples = 3, ?Distance $distanceMetric = null)
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{
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if ($distanceMetric === null) {
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$distanceMetric = new Euclidean();
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}
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$this->epsilon = $epsilon;
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$this->minSamples = $minSamples;
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$this->distanceMetric = $distanceMetric;
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}
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public function cluster(array $samples): array
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{
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$labels = [];
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$n = 0;
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foreach ($samples as $index => $sample) {
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if (isset($labels[$index])) {
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continue;
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}
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$neighborIndices = $this->getIndicesInRegion($sample, $samples);
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if (count($neighborIndices) < $this->minSamples) {
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$labels[$index] = self::NOISE;
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continue;
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}
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$labels[$index] = $n;
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$this->expandCluster($samples, $neighborIndices, $labels, $n);
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++$n;
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}
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return $this->groupByCluster($samples, $labels, $n);
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}
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private function expandCluster(array $samples, array $seeds, array &$labels, int $n): void
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{
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while (($index = array_pop($seeds)) !== null) {
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if (isset($labels[$index])) {
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if ($labels[$index] === self::NOISE) {
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$labels[$index] = $n;
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}
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continue;
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}
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$labels[$index] = $n;
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$sample = $samples[$index];
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$neighborIndices = $this->getIndicesInRegion($sample, $samples);
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if (count($neighborIndices) >= $this->minSamples) {
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$seeds = array_unique(array_merge($seeds, $neighborIndices));
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}
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}
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}
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private function getIndicesInRegion(array $center, array $samples): array
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{
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$indices = [];
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foreach ($samples as $index => $sample) {
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if ($this->distanceMetric->distance($center, $sample) < $this->epsilon) {
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$indices[] = $index;
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}
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}
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return $indices;
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}
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private function groupByCluster(array $samples, array $labels, int $n): array
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{
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$clusters = array_fill(0, $n, []);
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foreach ($samples as $index => $sample) {
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if ($labels[$index] !== self::NOISE) {
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$clusters[$labels[$index]][$index] = $sample;
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}
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}
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// Reindex (i.e. to 0, 1, 2, ...) integer indices for backword compatibility
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foreach ($clusters as $index => $cluster) {
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$clusters[$index] = array_merge($cluster, []);
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}
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return $clusters;
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}
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}
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