[{'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:# set up a merge for stations 1 and 2\n# keep unique cols from station 2\nkeep_cols = ['Date', u'Tmax', u'Tmin', u'Tavg',u'PrecipTotal']\ntrain_station_2 = train_station_2[keep_cols]\ntest_station_2 = test_station_2[keep_cols]\n\n# rename cols with prefix\nprefix_s2 = 'stat_2_'\nrename_cols_s2 = [prefix_s2 + col for col in train_station_2.columns]\ntrain_station_2.columns = rename_cols_s2\ntest_station_2.columns = rename_cols_s2"}, {'role': 'assistant', 'content': 'data_preprocessing'}]