[{'role': 'system', 'content': "You are an expert in machine learning and your task is to classify code snippets into one of the following categories: ['helper_functions', 'load_data', 'data_exploration', 'data_preprocessing', 'evaluation', 'modelling', 'prediction', 'result_visualization', 'save_results', 'comment_only']."}, {'role': 'user', 'content': "Identify the single most appropriate category to which the provided code belongs. Provide your response as a single category label without any additional information, commentary, or personal opinions.\\nPython Code:month = 5\nyear = 2011\nstart_date = datetime.datetime(year, month, 1, 0, 0, 0)\nend_date = datetime.datetime(year, month, 19, 23, 0, 0)\n# train_data['count_log'] = np.log1p(train_data['count'])\n# train_data['rolling_mean'] = train_data['count'].rolling(window = 24).mean()\n# train_data['rolling_std'] = train_data['count'].rolling(window = 24).std()\n"}, {'role': 'assistant', 'content': 'helper_functions'}]