[{'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:emails1999 = emails[emails[\'date\'] >= pd.datetime(1999,1,1)]\nemails1999 = emails1999[emails1999[\'date\'] < pd.datetime(2000,1,1)]\nemails2000 = emails[emails[\'date\'] >= pd.datetime(2000,1,1)]\nemails2000 = emails2000[emails2000[\'date\'] < pd.datetime(2001,1,1)]\nemails2001 = emails[emails[\'date\'] >= pd.datetime(2001,1,1)]\nemails2001 = emails2001[emails2001[\'date\'] < pd.datetime(2002,1,1)]\nemails2002 = emails[emails[\'date\'] >= pd.datetime(2002,1,1)]\nemails2002 = emails2002[emails2002[\'date\'] < pd.datetime(2003,1,1)]\nemails2003 = emails[emails[\'date\'] >= pd.datetime(2003,1,1)]\nemails2003 = emails2003[emails2003[\'date\'] < pd.datetime(2004,1,1)]\nemails2004 = emails[emails[\'date\'] >= pd.datetime(2004,1,1)]\nemails2004 = emails2004[emails2004[\'date\'] < pd.datetime(2005,1,1)]\nnumberofemailsperyear = pd.DataFrame()\nnumberofemailsperyear[\'Year\'] = ["1999","2000","2001","2002","2003","2004"]\nnumberofemailsperyear[\'Number of Emails\'] = [len(emails1999),len(emails2000),len(emails2001),len(emails2002),len(emails2003),len(emails2004)]\nnumberofemailsperyear = numberofemailsperyear.set_index(\'Year\')'}, {'role': 'assistant', 'content': 'data_preprocessing'}]