arrays don't merge

[Kokos Koka]

I have a photo album, with a 'photos' field in database which has serialized data and is base 64 encoded. I can upload up to 21 photos at the same time for the album (multiple uploading). When trying to add new photos to the album on edit mode, I can't get the new $_FILES array to merge with the old array in the database. I want to update only the values that I have changed. So let's say I already had 2 images inside my album, I would like to add a 3rd image without losing the other 2 images. Here's my code:

if (isset($_REQUEST['action']) && $_REQUEST['action'] == 'edit') {
        //select photo album and get photos and descriptions to be merged with new.
        $album_id           = $_REQUEST['album_id'];    
        $old_photos         = null;
        $old_descriptions   = null;

        $getAlbumQ = mysql_query("select * from albums where id='$album_id'");

        while ($old_album = mysql_fetch_array($getAlbumQ)) {
            $old_photos         = unserialize(base64_decode($old_album['photos']));
            $old_descriptions   = unserialize(base64_decode($old_album['descriptions']));
        }

        if (isset($_POST['album_name']) && isset($_POST['desc'])) {
            $name       = $_POST['album_name'];
            $desc       = $_POST['desc'];
            $idesc      = array();
            $target_path = "../uploads/albums/";



            foreach ($_FILES as $k => $v) {
                //first upload photos
                $path = $target_path . basename($v['name']); 
                if(move_uploaded_file($v['tmp_name'], $path)) {

                    $hasUpload = true;
                }   
            }



            for ($j = 1; $j < 21; $j++) {
                    $img_index  = $j;
                    $img_desc   = $_POST['desc_' . $img_index];

                    array_push($idesc, $img_desc);          

            }

           foreach ($_FILES as $key => $value) {
     
                        foreach ($value as $k => $v) {
                             if ($k === 'name' && $v !== '') {
                                 break;
                             } else {
                                 unset($_FILES[$key]);
                             }
                        }
            }


            for ($i = 1; $i < 21; $i++) {


            if($_FILES['image_'.$i]['name']!= '')
            {
            $hasUpload = true;

            $presults       = array_merge($old_photos, $_FILES); //THE PROBLEM WITH MERGING ARRAYS OCCURS HERE
            $dresults       = array_merge($old_descriptions, $idesc);

            $images         = base64_encode(serialize($presults));
            $descriptions   = base64_encode(serialize($dresults));
            $posted         = date("Y-m-d H:i:s");
            }
            else {
                $hasUpload = false;

            $presults       = $old_photos;
            $dresults       = $idesc;

            $images         = base64_encode(serialize($presults));
            $descriptions   = base64_encode(serialize($dresults));
            $posted         = date("Y-m-d H:i:s");
            }
        }

        }
    }

[Kokos Koka]

Just needed to add the following lines of code outside the for ($i = 1; $i < 21; $i++) loop:

//delete empty values for $_FILES array

foreach ($_FILES as $key => $value) {

                    foreach ($value as $k => $v) {
                         if ($k=='name' && $v!='') {
                             break;
                         } else {
                             unset($_FILES[$key]);
                         }
                   }
                 }

//custom array merge function 

function merge(&$a, &$b){
   $keys = array_keys($a);
   foreach($keys as $key){
       if(isset($b[$key])){
           if(is_array($a[$key]) and is_array($b[$key])){
               merge($a[$key],$b[$key]);
           }else{
               $a[$key] = $b[$key];
           }
       }
   }
   $keys = array_keys($b);
   foreach($keys as $key){
       if(!isset($a[$key])){
           $a[$key] = $b[$key];
       }
   }
}

then instead of array_merge(), I used merge() inside the for ($i = 1; $i < 21; $i++) loop:

$presults       = merge($old_photos, $_FILES);