$data['query'] result to form_dropdown()

[eluser]dimaomni[/eluser]
Hello Dear.
I have stuck with passing data from Controller to Viewer.
How to make dropdawn menu with combined number.letter column?
print_r($query) in viewer gives below result:
Array
(
[0] => stdClass Object
(
[id] => 1
[number] => 8
[letter] => A
)
[1] => stdClass Object
(
[id] => 9
[number] => 8
[letter] => B
)
[2] => stdClass Object
(
[id] => 10
[number] => 8
[letter] => V
)
-------------------
Controller:
...
$data['query'] = $this->Meditlesson->selectclass();
$this->load->view('admin/vshowbylesson',$data);
...

View:
..
echo form_dropdown('classroom', $query, '1')
...
Thanks in advance!