codeigniter dependent dropdown error

Controller

public function ajax_get_subgroup()
{
extract($_POST);
$tmp='';
$sql = "SELECT * FROM cat_shopping_group where group_shop_id=$id";
$data = $this->db->query($sql)->result_array();
$tmp .="<option value=''>-- Select --</option>";
foreach($data as $row)
{
$tmp .="<option value='".$row['your_id']."'>".$row['cat_shop_name ']."</option>";
}
die($tmp);
}`
AJAX

function get_data()
{
var id = $('#senf').val()

datana= 'id='+id
$.ajax({
type: 'POST',
url: '<?=base_url()?>your_controller/ajax_get_subgroup',
data: datana,
error: function(data) {
alert('Failed');
},
success: function(data)
{
$('#raste').html(data)
}
})
}
Views

<select id="senf" name="group" onchange='ajax_get_subgroup();'>
<option value="" selected="selected">select</option>
<?php
your code
?>
</select>
<select id="raste">
</select>
Hope this help.