[{'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:trainData[\'Open Date\'] = pd.to_datetime(trainData[\'Open Date\'], format=\'%m/%d/%Y\')   \ntestData[\'Open Date\'] = pd.to_datetime(testData[\'Open Date\'], format=\'%m/%d/%Y\')\n\ntrainData[\'OpenDays\']=""\ntestData[\'OpenDays\']=""\n\ndateLastTrain = pd.DataFrame({\'Date\':np.repeat([\'01/01/2015\'],[len(trainData)]) })\ndateLastTrain[\'Date\'] = pd.to_datetime(dateLastTrain[\'Date\'], format=\'%m/%d/%Y\')  \ndateLastTest = pd.DataFrame({\'Date\':np.repeat([\'01/01/2015\'],[len(testData)]) })\ndateLastTest[\'Date\'] = pd.to_datetime(dateLastTest[\'Date\'], format=\'%m/%d/%Y\')  \n\ntrainData[\'OpenDays\'] = dateLastTrain[\'Date\'] - trainData[\'Open Date\']\ntestData[\'OpenDays\'] = dateLastTest[\'Date\'] - testData[\'Open Date\']\n\ntrainData[\'OpenDays\'] = trainData[\'OpenDays\'].astype(\'timedelta64[D]\').astype(int)\ntestData[\'OpenDays\'] = testData[\'OpenDays\'].astype(\'timedelta64[D]\').astype(int)\n\ntrainData = trainData.drop(\'Open Date\', axis=1)\ntestData = testData.drop(\'Open Date\', axis=1)\''}, {'role': 'assistant', 'content': 'data_preprocessing'}]