[{'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:recent_t = t_copy[(t_copy.DEED_TYPE=='Sheriffs Deed') & (t_copy.mdate > dt.datetime(2006,1,1))]\\\n.groupby('PROPERTY_NUMBER').first()\ndf = pd.merge(df, recent_t[['mdate']], how='left', left_on='parcel', right_index=True)\ndf.loc[df.mdate.isnull(),'mdate'] = dt.datetime(2006,1,1)\ndf['mdate'] = (df.Date-df.mdate).astype(pd.Timedelta).apply(lambda x: x.days)\ndf = df.rename(columns={'mdate':'t_shf_deed'})"}, {'role': 'assistant', 'content': 'data_preprocessing'}]