[{'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:def solution(key):\nkey = tuple(key)\nproduct_id = key[0]\nchannel_id = key[1]\nstore_id = key[2]\ndepot_id = key[3]\nif (product_id, depot_id, store_id) in logmeans_prod_depot_store:\nval = logmeans_prod_depot_store[product_id, depot_id, store_id]\nelif (product_id, store_id) in logmeans_prod_store:\nval = logmeans_prod_store[product_id, store_id]\nelif (product_id, channel_id, store_id) in logmeans_prod_chan_store:\nval = logmeans_prod_chan_store[product_id, channel_id, store_id]\nelif (product_id, depot_id) in logmeans_prod_depot:\nval = logmeans_prod_depot[product_id, depot_id]\nelif (product_id, channel_id) in logmeans_prod_chan:\nval = logmeans_prod_chan[product_id, channel_id]\nelif product_id in logmeans_prod:\nval = logmeans_prod[product_id]\nelse:\nval = log_global_median\nreturn val\nx_valid["log_guess"] = x_valid[["product_id", "channel_id", "store_id", "depot_id"]].apply(lambda x:solution(x), axis = 1)\ndisplay(str(rmse(x_valid["log_guess"], x_valid["log_demand"])))\nx_valid["guess"] = np.expm1(x_valid["log_guess"]) * exp_constant'}, {'role': 'assistant', 'content': 'data_preprocessing'}]