public function listBox($id)
 {
     $unique = PayrollHeading::distinctCompensations();
     if ($id != '') {
         $unique = array(0);
     }
     $compensations = self::activeCompensation()->whereNotIn('id', $unique)->orderBy('code')->get();
     $rows = array('0' => '');
     foreach ($compensations as $compensation) {
         $rows[$compensation->id] = $compensation->code;
     }
     return $rows;
 }