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