二维数组转换成一维数组

<?php
$arr=array(array('dw.html'),array("dz.html"));
echo "<pre />";
print_r($arr);
foreach($arr as $key => $val) {
    foreach($val as $value) {
        $new_arr[$key] = $value;
    }
}
print_r(implode(",", $new_arr));