Codeigniter agrupar e criar array multidimensional

function get_job(){
    $data   = array();
    $data   = $this->db->get('job')->result_array();
    foreach( $data as $key=>$each ){
        $data[$key]              = $this->db->where('idadministrator', $each['idadministrator'])->get('administrator')->row_array();
        $data[$key]['artwork']   = $this->db->where('idjob', $each['idjob'])->get('artwork')->result_array();  
    }
    return $data;
}