สอบถาม error Undefined offset: 6 ครับ ต้องแก้ไขยังไงครับ

$catid_ar = array();
$catname_ar = array();  
                
	if($row["category_id"]!=""){
					
		$catid_ar=explode(',',$row["category_id"]);
		$catname_ar=explode(',',$row["category_name"]);
                for($j=0;$j<count($catid_ar);$j++){
					  
		      $result .= '"id":"'.$catid_ar[$j].'",';
	              $result .= '"name":"'.$catname_ar[$j].'",';
                .......................................
                .......................................
	}