[{'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 ref_user_pref(users_pref_df):\nfeatures = users_pref_df.columns.tolist()\nfavorite_categories = users_pref_df[users_pref_df.index == reco_user]\nfavorite_categories_dict = dict()\nfor feature in features:\nfavorite_categories_dict[feature] = favorite_categories[feature].values[0]\nreco_user_preferences = sorted(favorite_categories_dict.items(), key = lambda t:t[1])\nuser_preferences_dict = dict()\nfor item in reco_user_preferences:\nif item[1] != 0:\nuser_preferences_dict[item[0]] = item[1]\nelse:\ncontinue\nreturn user_preferences_dict'}, {'role': 'assistant', 'content': 'data_preprocessing'}]