[{'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:string_dict = {'no data':-1,\n'poor':0,\n'satisfactory':1,\n'good': 2,\n'excellent':3,\n'yes': 1,\n'no': 0,\n'Investment': 1,\n'OwnerOccupier': 0}\nfor key in [key for key in dict(train_df.dtypes) if dict(train_df.dtypes)[key] in ['O'] and key != 'sub_area']:\ntrain_df[key] = train_df[key].map(string_dict)"}, {'role': 'assistant', 'content': 'data_preprocessing'}]