[{'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:df_traintest3 = []\nfor place in places[:]:\n    df_tmp = df_traintest2[df_traintest2['place_id']==place].reset_index(drop=True)\n    df_tmp = do_aggregations(df_tmp)\n    df_traintest3.append(df_tmp)\ndf_traintest3 = pd.concat(df_traintest3).reset_index(drop=True)\ndf_traintest3[df_traintest3['place_id']=='China/Hubei'].head()"}, {'role': 'assistant', 'content': 'data_preprocessing'}]