public function join(array $array, string $pkey, string $fkey): CollectionInterface
    {
        return $this->map(
            function ($item) use ($array, $pkey, $fkey) {
                foreach ($array as $value) {
                    if ($item[$pkey] == $value[$fkey]) {
                        return array_merge($item, $value);
                    }
                }
            }
        );
    }