PHP删除指定字符。该如何解决

$d = array(  0 => array(    'a' => string 'Days_3' (length=6)    'b' => string '3 Days' (length=6)  )  1 => array(    'a' => string 'Days_7' (length=6)    'b' => string '7 Days' (length=6)  )  2 => array(    'a' => string 'Days_14' (length=7)    'b' => string '14 Days' (length=7)  )  3 => array(    'a' => string 'Days_30' (length=7)    'b' => string '30 Days' (length=7)  )  4 => array(    'a' => string 'Days_60' (length=7)    'b' => string '60 Days' (length=7)  ));foreach($d as $v){    echo ltrim($v['a'],"Days_").",";}

$ch = '';foreach($d as $v){    echo $ch . ltrim($v['a'],"Days_");    $ch = ',';}
------解决方案--------------------
substr($str,0,-1)或者放入数组中。再用implode连接