Magento Event Observer按类别对产品集合进行分组

Question

我正在创建一个事件观察者模块，它将按类别对产品进行分组，

下面是我的模块的model / observer.php文件，

public function updateUpsells($observer)
    {
        $iCurrentCategory = Mage::registry('current_category')->getId();
        $event = $observer->getEvent();
        $oUpsellCollection = $event->getCollection();
        foreach ($oUpsellCollection->getItems() as $key => $oUpsellProduct) {
            $aCategoriesIds = $oUpsellProduct->getCategoryIds();
            if (!in_array($iCurrentCategory, $aCategoriesIds)) {
                $oUpsellCollection->removeItemByKey($key);
            }
        }
    }
}

启用此模块后，我可以通过echo upsell product's category id's

在upsell.phtml文件中加入$this->getItemCollection()->getItems()

因此我得到了，

    Array
(
    [170] => Mage_Catalog_Model_Product Object
        ( 
           .........................
           [_data:protected] => Array
                (
                    [entity_id] => 170
                    [entity_type_id] => 10
                    [attribute_set_id] => 44
                    [type_id] => simple
                    [category_ids] => Array
                        (
                            [0] => 12
                            [1] => 26
                        )
                    .......................

           )
    [171] => Mage_Catalog_Model_Product Object
        ( 
           .........................
           [_data:protected] => Array
                (
                    [entity_id] => 171
                    [entity_type_id] => 10
                    [attribute_set_id] => 44
                    [type_id] => simple
                    [category_ids] => Array
                        (
                            [0] => 16
                            [1] => 24
                        )
                    .......................

           )
)

所以现在我如何按类别对此数组结果进行分组。示例提到了2个分销到4个不同类别的追加销售产品，因此我需要对产品进行分组，例如，

Category id 12
  product1 | Product2

Category id 26
  product1 | Product2