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MedianAbsoluteError.php
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MedianAbsoluteError.php
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<?php
namespace Rubix\ML\CrossValidation\Metrics;
use Rubix\ML\Tuple;
use Rubix\ML\EstimatorType;
use Rubix\ML\Helpers\Stats;
use Rubix\ML\Specifications\PredictionAndLabelCountsAreEqual;
/**
* Median Absolute Error
*
* Median Absolute Error (MAD) is a robust measure of error, similar to MAE, that ignores
* highly erroneous predictions. Since MAD is a robust statistic, it works well even when
* used to measure non-normal distributions.
*
* > **Note:** In order to maintain the convention of *maximizing* validation scores,
* this metric outputs the negative of the original score.
*
* @category Machine Learning
* @package Rubix/ML
* @author Andrew DalPino
*/
class MedianAbsoluteError implements Metric
{
/**
* Return a tuple of the min and max output value for this metric.
*
* @return \Rubix\ML\Tuple{float,float}
*/
public function range() : Tuple
{
return new Tuple(-INF, 0.0);
}
/**
* The estimator types that this metric is compatible with.
*
* @internal
*
* @return list<\Rubix\ML\EstimatorType>
*/
public function compatibility() : array
{
return [
EstimatorType::regressor(),
];
}
/**
* Score a set of predictions.
*
* @param list<int|float> $predictions
* @param list<int|float> $labels
* @throws \Rubix\ML\Exceptions\InvalidArgumentException
* @return float
*/
public function score(array $predictions, array $labels) : float
{
PredictionAndLabelCountsAreEqual::with($predictions, $labels)->check();
if (empty($predictions)) {
return 0.0;
}
$errors = [];
foreach ($predictions as $i => $prediction) {
$errors[] = abs($labels[$i] - $prediction);
}
return -Stats::median($errors);
}
/**
* Return the string representation of the object.
*
* @internal
*
* @return string
*/
public function __toString() : string
{
return 'Median Absolute Error';
}
}