[{'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_hiv_to_add = df_HIV\ndf_hiv_to_add['Year'] = df_hiv_to_add['Year'].apply(pushHIV)\ndf_hiv_to_add = df_hiv_to_add[(df_hiv_to_add.Year != '2009') & (df_hiv_to_add.Year != '2005') ]\ndf_le_to_add = df_le_clean\ndf_le_to_add = df_le_to_add[(df_le_to_add.Year != '1990') & (df_le_to_add.Year != '2012')]\ndf_hs_to_add = df_hs\ndf_hs_to_add['Year'] = df_hs_to_add['Year'].apply(pushHIV)\ndf_hs_to_add =df_hs_to_add[(df_hs_to_add.Year!='2012')]"}, {'role': 'assistant', 'content': 'data_preprocessing'}]