To extract grouped results, we will add the _get_average_cost method, which will use the read_group() method to fetch the data in a group:

    @api.model
    def _get_average_cost(self):
        grouped_result = self.read_group(
            [('cost_price', "!=", False)], # Domain
            ['category_id', 'cost_price:avg'], # Fields to access
            ['category_id'] # group_by
            )
        return grouped_result

To test this implementation, you need to add a button in the user interface that triggers this method.