YII CGRIDVIEW drop down filter

 <?php  
 $this->widget('zii.widgets.grid.CGridView', array(  
   'itemsCssClass' => 'table table-hover table-striped table-bordered table-condensed',  
   'id' => 'orders-grid',  
   'dataProvider' => $model->search(),  
   'filter' => $model,  
   'columns' => array(  
     'order_id',  
     'user_id',  
     array(  
       'header' => 'Product Name (QTY)',  
       'value' => 'OcProductDescription::model()->order_products("$data->offer_ids")',  
     ),  
     'offer_ids',  
     'order_total',  
     'order_status',  
     'payment_status',  

// this code below is used to create drop down filter
     array(  
       'name' => 'affiliate',  
       'value' => 'Orders::model()->getAffiliateValue($data->affiliate)',  
       'filter' => array(  
         '1' => 'ΓΑΙΤΑΝΗΣ ΒΑΣΙΛΕΙΟΣ',  
         '2' => 'ΘΕΟΔΩΡΟΣ ΚΑΜΠΟΛΗΣ',  
         '3' => 'ΑΘΗΝΑ ΦΡΑΓΚΟΥ',  
       )  
     ),  
     'order_date',  
     array(  
       'class' => 'CButtonColumn',  
     ),  
   ),  
 ));  
 ?>