How to get form_dropdown() show the selected value in Codeigniter?

I am trying to populate a dropdown list from database. In my view file I have the following code

$batch= $query ['batch']; // I pull this data from a separate model 
echo form_dropdown('shirts', $options, $batch);

Now the drop down list is populating data fine but the problem is I don't get the value-"$batch" automatically selected when the page loads. Interestingly if I echo $batch, elsewhere in the page it shows the correct data, which means $batch is okay.

Here is my Controller

function update($id){
$this->load->model('mod_studentprofile');
             $data['query']= $this->mod_studentprofile->student_get($id);
             $data['options']= $this->mod_studentprofile->batchget();

             $data['tab'] = "Update Student Information";
                 $data['main_content']='update_studentprofile';
                 $this->load->view('includes/template',$data);
            }

And here is my model

 function batchget() {

      $this->db->select('batchname');
       $records=$this->db->get('batch');

            $data=array();

                        foreach ($records->result() as $row)
                {
                    $data[$row->batchname] = $row->batchname;
                }

            return ($data);
        }

Would you please kindly help me to solve this problem. I want to have the value- "$batch" automatically selected in the dropdown list when the page loads.

Thanks in Advance.

EDit... my Model for student_get($id)

  function student_get($id)
    {
        $query=$this->db->get_where('student',array('studentid'=>$id));
        return $query->row_array();
    }

Thanks :)

Solution

I think that what's probably happening is that the value in $batch may be matching what's rendering in the dropdown but not the actual key in $options for that particular option which would be the value="" portion of the html.

for example...

// this wouldn't select 'foo' as you may be thinking
$options => array('0' => 'foo', '1' => 'bar');
$batch = 'foo';
echo form_dropdown('shirts', $options, $batch);

// this would select foo
$options => array('foo' => 'foo', 'bar' => 'bar');
$batch = 'foo';
echo form_dropdown('shirts', $options, $batch);

Edit in response to OP's comment:

The batchget() method looks like it returns your $options array in the proper format and your student_get() method is returning a row_array. It appears that in the view you're assigning the value of one of the keys returned by the student_get method to be the selected value stored in $batch which is then passed in as the third argument to form_dropdown().

This all appears to be correct. As long as the value of $batch is indeed one of the array keys that is in $options then form_dropdown() will set one of the dropdown options as having been selected.