Mage_CatalogSearch_Block_Result:_getProductCollection()

protected function _getProductCollection()
{
    if (is_null($this->_productCollection)) {
        $this->_productCollection = $this->getListBlock()->getLoadedProductCollection();
    }
    $activeCategories = Mage::getResourceModel('catalog/category_collection')
    ->addAttributeToFilter('is_active', 1)
    ->getColumnValues('entity_id');

    $this->_productCollection->joinField(
        'category_id', 'catalog/category_product', 'category_id',
        'product_id = entity_id', null, 'left'
    )
    ->addAttributeToSelect('*')
    ->addAttributeToFilter('category_id', array(
            array('in' => $activeCategories),
    ));
    $this->_productCollection->getSelect()->group('entity_id');
    // echo "<pre>";
    // print_r($this->_productCollection->getData());
    // die;
    return $this->_productCollection;
}