Add categories column to the product grid in Magento admin

Question

I\'m trying to add a category column to the product grid. I\'ve modified Mage_Adminhtml_Block_Catalog_Product_Grid. Added the following to _prepareCollection<

Answer 1

to display the name o all categories you can use

$this->addColumn('category_ids',
        array(
                                    'header'=> Mage::helper('catalog')->__('Category'),
                                    'type'  => 'options',
                                    'index' => 'category_ids',
                                    'options' => $this->catOptions,
                                    'renderer'  => 'Your_Module_Block_Adminhtml_List_Cat',
));

in your class block

 class Your_Module_Block_Adminhtml_List_Cat extends Mage_Adminhtml_Block_Widget_Grid_Column_Renderer_Abstract
{
    public function render(Varien_Object $row)
    {
        $product = Mage::getModel('catalog/product')->load($row->getEntityId());
        $cats = $product->getCategoryIds();
        $allCats = '';
        foreach($cats as $key => $cat)
        {
            $_category = Mage::getModel('catalog/category')->load($cat);
            $allCats.= $_category->getName();
            if($key < count($cats)-1)
                $allCats.= ' ,';
        }
        return $allCats;
    }

}