[{'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:mean_error = []\nfor day in range(2, train_baseline.Day.max() + 1):\n    val = train_baseline[train_baseline.Day == day]\n    p = val.Last_Week_Sales.values\n    error = rmspe(val.Sales.values, p)\n    mean_error.append(error)\n    \nprint('Mean Error = %.5f' % np.mean(mean_error))"}, {'role': 'assistant', 'content': 'data_preprocessing'}]