[{'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:all_males_allincomes = np.array(\nnp.concatenate([allmales['all']['Median income'][:].values,\nallmales['white']['Median income'][:].values,\nallmales['black']['Median income'][:].values,\nallmales['hispanic']['Median income'][:].values,\nallmales['asian']['Median income'][:].values]).flatten())\nall_females_allincomes = np.array(\nnp.concatenate([allfemales[k]['Median income'][:].values \\\nfor k in ['all',\n'white', 'black',\n'hispanic', 'asian']]).flatten())\nmask = ~(np.isnan(all_males_allincomes) + np.isnan(all_females_allincomes))"}, {'role': 'assistant', 'content': 'data_preprocessing'}]