foreach覆盖消息数据php的每次迭代

我获取消息的mySQL数据的内容，然后按每个用户对其进行排序，以创建一个通用的消息数组。

理想如此：

 Array(
    ["Mr.EasyBB"] => Array(
                    [0] => array(//message data here)
                    [1] => array(//message data here)
                    ...
                  );
 );

PHP到目前为止

 $messages = $controller->loadResult(
     "SELECT * FROM messages WHERE from_username='$username' AND from_uid='$uid'"
     );
 if($messages){
    foreach($messages as $data){
       $to_username = strtolower($data["to_username"]);
          if(!in_array($to_username,$conversations)){
              $conversations[$to_username] = array();
          } 
         $conversations[$to_username][]= $data;
    }

虽然我的输出是

 Array
 (
  [ianbruce] => Array
      (
        [0] => Array
            (
                [0] => 231
                [to_uid] => 231
                [1] => 0001
                [from_uid] => 0001
                [2] => IanBruce
                [to_username] => IanBruce
                [3] => Mr.EasyBB
                [from_username] => Mr.EasyBB
                [4] => n
                [deleted] => n
                [5] => n
                [sent_deleted] => n
                [6] => Howdy Again my Friend
                [message] => Howdy Again my Friend
                [7] => 2014-10-18 00:01:04
                [to_timestamp] => 2014-10-18 00:01:04
                [8] => 0000-00-00 00:00:00
                [from_timestamp] => 0000-00-00 00:00:00
                [9] => y
                [from_seen] => y
                [10] => n
                [to_seen] => n
            )
        )
    )

现在我知道它要么覆盖用户内部的数组，要么完全覆盖用户，使其显示数组的最后一次推送。不确定我在这里做错了什么，我想也许一双新的眼睛会有所帮助。