[{'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:\nfor col in dftrain.columns:\n    if (dftrain[col].dtype == int) | (dftrain[col].dtype == float):\n        if col not in ['P2','P3', 'P7','revenue']:\n            dftrain[col] = dftrain[col].map(lambda x:np.log1p(x))\n            print (col)\n            dftest[col] = dftest[col].map(lambda x: np.log1p(x))\n            "}, {'role': 'assistant', 'content': 'data_preprocessing'}]