php-ml/src/Phpml/Math/Distance/Euclidean.php

<?php

declare(strict_types=1);

namespace Phpml\Math\Distance;

use Phpml\Exception\InvalidArgumentException;
use Phpml\Math\Distance;

class Euclidean implements Distance
{
    /**
     * @param array $a
     * @param array $b
     *
     * @return float
     *
     * @throws InvalidArgumentException
     */
    public function distance(array $a, array $b): float
    {
        if (count($a) !== count($b)) {
            throw InvalidArgumentException::arraySizeNotMatch();
        }

        $distance = 0;

        foreach ($a as $i => $val) {
            $distance += ($val - $b[$i]) ** 2;
        }

        return sqrt((float) $distance);
    }
}