Proyectos de Subversion Moodle

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<?php
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declare(strict_types=1);
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namespace Phpml\FeatureSelection;
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use Phpml\Exception\InvalidArgumentException;
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use Phpml\Math\Matrix;
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use Phpml\Math\Statistic\Variance;
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use Phpml\Transformer;
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final class VarianceThreshold implements Transformer
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{
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    /**
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     * @var float
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     */
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    private $threshold;
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    /**
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     * @var array
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     */
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    private $variances = [];
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    /**
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     * @var array
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     */
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    private $keepColumns = [];
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    public function __construct(float $threshold = 0.0)
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    {
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        if ($threshold < 0) {
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            throw new InvalidArgumentException('Threshold can\'t be lower than zero');
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        }
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        $this->threshold = $threshold;
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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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        $this->variances = array_map(static function (array $column): float {
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            return Variance::population($column);
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        }, Matrix::transposeArray($samples));
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        foreach ($this->variances as $column => $variance) {
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            if ($variance > $this->threshold) {
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                $this->keepColumns[$column] = true;
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            }
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        }
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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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        foreach ($samples as &$sample) {
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            $sample = array_values(array_intersect_key($sample, $this->keepColumns));
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        }
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    }
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}