protected function resample(): array
    {
        $weights = $this->weights;
        $std = StandardDeviation::population($weights);
        $mean = Mean::arithmetic($weights);
        $min = min($weights);
        $minZ = (int) round(($min - $mean) / $std);

        $samples = [];
        $targets = [];
        foreach ($weights as $index => $weight) {
            $z = (int) round(($weight - $mean) / $std) - $minZ + 1;
            for ($i = 0; $i < $z; ++$i) {
                if (random_int(0, 1) == 0) {
                    continue;
                }

                $samples[] = $this->samples[$index];
                $targets[] = $this->targets[$index];
            }
        }

        return [$samples, $targets];
    }