How do I add a custom dropdown filter in a grid

Question

This is my code:

   $this->addColumn(
       $key,
       array(
           header' => Mage::helper('core')->__($key),
           'index' => $key,
           'filter' => 'adminhtml/widget_grid_column_filter_select',
           'sortable' => true,
       )
   );      

I want to get all of the values from my column and put it in the dropdown options values and to filter them. Is there a way to do that ? At the moment I got an empty dropdown.

[UPDATE]

For instance if my values are 2,3,2,3,4,5,6,7 . I want to have in my dropdown the following values: 2,3,4,5,6,7

[UPDATE 2]

I managed to put the values in the dropdown. See My code:

$this->addColumn(
    $key,
    array(
       'header' => Mage::helper('core')->__($key),
       'index' => $key,
       'filter' => 'adminhtml/widget_grid_column_filter_select',
       'sortable' => true,
       'renderer' => $render,
       'type'      => 'options',
       'options'   => $this->_getOrderType(),
      )
);
public function _getOrderType(){
        $types = new Varien_Object(array(
            "Frontend" => "Frontend",
            "AdminPanel" => "AdminPanel"
        ));
        return $types->getData();
}

But my filter doesn't work. If I filter after smth I got an empty grid.

[UPDATE 3]

Update with the render function:

public function render(Varien_Object $row)
    {
        $value = $this->_getValue($row);
        if ($value == ""){
            return "Frontend";
        }else {
            return "AdminPanel";
        }
    }

Answer 1

I am not sure where the values come from, but you can use native's php array_unique function on the array of values, so the options would be unique.

Answer 2

You can simply use as below

$this->addColumn($key, array(
        'header' => Mage::helper('core')->__($key),
        'align' => 'left',
        'width' => '80px',
        'index' => 'status',
        'type' => 'options',
        'options' => array(
            'Frontend' => 'Frontend',
            'Admin' => 'Admin'
        )
    ));