ต้องการ explode ค่าที่อยู่ในตัวแปร $tri_nGRamคะ ลองทำแล้ว ไม่ได้อ่ะคะ คัยรู้ช่วยนะนำหน่อยคะ

$tri_nGRam = tri_nGRam($str_new);//ค้นสามคำในDB
$ar = explode('|',$tri_nGRam);
$a=$ar [0];
$b=$ar [1];
//echo $a.$b;
			
//========================================================

function tri_nGRam($str_new)//3-gramDB
{	
		$a = "";
		$b = "";
		$c = "";
		echo"3-GramDB"."<br>";
		foreach($str_new as $k => $v)
		{
			if (strlen($v)>0) 
			{
				if (strlen($a)<=0) $a = $v;
				elseif (strlen($b)<=0) $b = $v;
				elseif (strlen($c)<=0) 
				{ 
					$c = $v;
					
					$triGram=$a.$b.$c;
					$sql="select * from trigram where w_one ='$a' AND w_two='$b' AND w_three='$c'";
					$result = mysql_query($sql ) or die(mysql_error());
					//echo $sql."<br>"; 
					$row = mysql_num_rows($result);
				
					if ($row>0)
					{
						$table = mysql_fetch_array($result);
						$frequency_tri =$table["frequency"];
						$w_one=$table["w_one"];
						$w_two=$table["w_two"];
						$w_three=$table["w_three"];
						$WordtriGram=$w_one.$w_two.$w_three;
						$str_tri=$frequency_tri.'|'.$WordtriGram;
						
					
					}
					else 
					{
						echo "NOT-FOUND: ".$triGram."<br>";
						
					}
				$a = $b;
				$b = $c;
				$c = ""; 
		              $er[]=$str_tri.'|'.$triGram;
				
		
		}	
	} 
} 
	
	return $er;
	
}