php如何去除字符串的相同项

<?php
header('content-type:text/html;charset=utf-8');   
$str = "1234123aab3n4";
echo "原字符串：".$str."<br><br>";
 
$arr=str_split($str);
echo "字符数组：";
var_dump($arr);

$newArr=array_flip(array_flip($arr));
echo "去重后的数组：";
var_dump($newArr);
$newStr=implode("",$newArr);
echo "去重后的字符串：".$newStr;
?>