如何为每个循环数组和调用函数？

I have an array that I need to loop through, and for specific keys, I then need to call chopActNum function. The function takes an account number, and turns it into the "xxxxxxxxxx1234" format. I would like to then display this new format rather than the whole account number. My $accountList holds all the information for the accounts. My confusion is in that I currently display all my account information through assignment in Smarty templating. I am horrible at explaining, so perhaps seeing my code will help elucidate my issue.
My function:

public function chopActNum($actNum=0){

    $numPlace=strlen($actNum)-4;
    $repeatX=str_repeat('x',$numPlace);
    $actNumConcat=$repeatX.substr($actNum, -4); 
    return $actNumConcat;

Php:

foreach($achList as $a)
{
$actNum[] = $a['actNum'];
$chopNum=$Ach->chopActNum($actNum);
}

$achList=$Ach->listAch($logged_userid);
$smarty->assign("accountList",$achList);

Tpl Code:

{foreach from=$accountList item=v name=foo} 
<td class="tableData">{$v.actName}</td>
<td class="tableData">{$v.actNum}</td>
<td class="tableData">{$v.bankRoute}</td>
{/foreach}

use array_map to prepare the data for your template like this:

$achList = arrar_map(function($v){
  return array(
    'actName' => $v['actName'],
    'actNum' => chopActNum($v['actNum']),
    'bankRoute' => $v['bankRoute']
  );
}, $achList);

You can get the key in foreach, and then check if it's one of the specific keys.

$specific_keys = array(...);
foreach ($achList as $key => $acct) {
    if (in_array($key, $specific_keys)) {
        $actNum[] = chopActNum($acct['actNum']);
    } else {
        $actNum[] = $acct['actNum'];
    }
}