[{'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:train[col4train] = train[col4train].values.astype(str)\ntest[col4train] = test[col4train].values.astype(str)\n\nfrom itertools import combinations\nnew_col4train = col4train\nfor c1,c2 in combinations(col4train, 2):\n    name = "{}_{}".format(c1,c2)\n    new_col4train.append(name)\n    train[name] = train[c1] + "_" + train[c2]\n    test[name] = test[c1] + "_" + test[c2]'}, {'role': 'assistant', 'content': 'data_preprocessing'}]