[{'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:# city_rev = []\n\n# for i in train['City']:\n#     for key, value in mean_dict.items():\n#         if i == key:\n#             city_rev.append(value)\n            \n# df_city_rev = pd.DataFrame({'city_rev':city_rev})\n# train = pd.concat([train,df_city_rev],axis=1)\n# train.head()"}, {'role': 'assistant', 'content': 'helper_functions'}]