[{'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_us = df_train[df_train['Country_Region']=='US']\ndf_us['Date'] = df_us['Date'].astype(str)\ndf_us['state_code'] = df_us.apply(lambda x: us_state_abbrev.get(x.Province_State,float('nan')), axis=1)\ndf_us['ln(ConfirmedCases)'] = np.log(df_us.ConfirmedCases + 1)\ndf_us['ln(Fatalities)'] = np.log(df_us.Fatalities + 1)"}, {'role': 'assistant', 'content': 'data_preprocessing'}]