Поменять картинки местами

$pics = $modx->getCollection('msProductFile', ['parent' => 0]);
foreach($pics as $pic) {
    $arr[$pic->toArray()['product_id']][] = $pic->toArray()['url'];
}
$vv;
foreach($arr as $k=>$ar){
  if(count($ar) > 1){
    $vv[$k] = array_reverse(array_slice($ar, 0, 2));
  }else{
    continue;
  }
}

foreach($pics as $pic) {
  if(!($vv[$pic->toArray()["product_id"]][0])) continue;
  
  $pic->set('url',$vv[$pic->toArray()["product_id"]][0]);
  $pic->save();
  if($bb = $vv[$pic->toArray()["product_id"]][0]){
   $vv[$pic->toArray()["product_id"]][0] = $vv[$pic->toArray()["product_id"]][1];
  }
}