[{'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:test_merged['Open']=test_merged['Open'].fillna(1)\ntest_merged['Date']=pd.to_datetime(test_merged['Date'],format='%Y-%m-%d')\ntest_merged['day']=test_merged['Date'].dt.day\ntest_merged['month']=test_merged['Date'].dt.month\ntest_merged['year']=test_merged['Date'].dt.year\n\n\ntest_merged['StateHoliday']=test_merged['StateHoliday'].map({'0':0,'a':1})\ntest_merged['StateHoliday']=test_merged['StateHoliday'].astype(int)\ntest_merged.isna().sum()"}, {'role': 'assistant', 'content': 'data_preprocessing'}]