[{'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:#    (   )\n# res_list_depth = []\n# res_list_nestim = []\n# for i in range (1, 1000, 50):\n#     store_part = train_stores[i]\n#     X_train_part = store_part.drop(["Sales", "Store", "Customers"],axis=1)\n#     Y_train_part = store_part["Sales"]\n#     X_train_part = X_train_part.fillna(X_train_part.mean())\n#     estimator = RandomForestRegressor(random_state=42, criterion = \\'}, {'role': 'assistant', 'content': 'helper_functions'}]