php 二维数组下,循环拼接字符串

以上数组为$teacher=array();

$v="";

for($i=0;$i<count($teacher["teacher_class"]);$i++){
    if(($i+1)==(count($teacher["teacher_class"]))){
        $v .= $teacher["teacher_class"][$i];
    }else{
        $v .= $teacher["teacher_class"][$i].",";
    }
}
$teacher["teacher_class"]=$v;

结果: