PHP 一維數組轉二維數組

<?php 
$asr[1] = array("a","b","c","d");
$asr[2] = array("a","b","c","d");
$asr[3] = array("a","b","c","d");
$newarray = array();
foreach($asr as $a)
{
$newarray[] = $a;
}
print_r($newarray);
?>