PDOStatement:execute - simplified $placeholder form

pdostatement.php

<?php 
/*
*from
* http://php.net/manual/en/pdostatement.execute.php#111823
* simplified $placeholder form 
*/

$data = ['a'=>'foo','b'=>'bar']; 

$keys = array_keys($data); 
$fields = '`'.implode('`, `',$keys).'`'; 

#here is my way 
$placeholder = substr(str_repeat('?,',count($keys)),0,-1); 

$pdo->prepare("INSERT INTO `baz`($fields) VALUES($placeholder)")->execute(array_values($data));

?>