[{'role': 'system', 'content': "You are an expert in machine learning and your task is to classify the code snippets into categories from the provided list of categories. List of categories: ['helper_functions', 'load_data', 'data_exploration', 'data_preprocessing', 'evaluation', 'modelling', 'prediction', 'result_visualization', 'save_results', 'comment_only']"}, {'role': 'user', 'content': "Identify to which category the provided code belongs and assign the code snippet to at least 1 but up to 5 categories based on the probabilities, ignore if the probability of the category is negligible. Strictly provide your response as a list. Avoid providing any additional information, commentary, or personal opinions.\\nPython Code:dftrain['Dayofyear'] = dftrain['Date'].dt.dayofyear\ndftest['Dayofyear'] = dftest['Date'].dt.dayofyear\ndftest['Expo'] = dftest['Dayofyear']-baseday\nprint(dftrain.tail(5))\ndftest = dftest.merge(dftrain[['Country_Region','Province_State','Date','ConfirmedCases','Fatalities']]\n                      , on=['Country_Region','Province_State','Date'], how='left', indicator=True)\n"}, {'role': 'assistant', 'content': "['data_preprocessing']"}]