[{'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 standard_units(any_numbers):\n"Convert any array of numbers to standard units."\nreturn (any_numbers - np.mean(any_numbers)) / np.std(any_numbers)\ndef standardize(t):\n"""Return a table in which all columns of t are converted to standard units."""\nt_su = Table()\nfor label in t.labels:\nt_su = t_su.with_column(label + \' (su)\', standard_units(t.column(label)))\nreturn t_su'}, {'role': 'assistant', 'content': 'data_preprocessing'}]