[{'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:fig, (axis1,axis2) = plt.subplots(1,2,figsize=(15,4))\naxis1.set_title('Original Age values')\naxis2.set_title('New Age values')\naverage_age   = data['custAge'].mean()\nstd_age      = data['custAge'].std()\ncount_nan_age = data['custAge'].isnull().sum()\nrand_1 = np.random.randint(average_age - std_age, average_age + std_age, size = count_nan_age)\ndata['custAge'].dropna().astype(int).hist(ax=axis1)\ndata['custAge'][np.isnan(data['custAge'])] = rand_1\ndata['custAge'] = data['custAge'].astype(int)\ndata['custAge'].hist(ax=axis2);"}, {'role': 'assistant', 'content': 'data_exploration'}]