[{'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:# Calculate percent of missing in each column\ncol_pct_miss = []\nfor col in df.columns:\n    percent_miss = np.mean(df[col].isnull())*100\n    if percent_miss > 0:\n        col_pct_miss.append([col, percent_miss])\n    \ncol_pct_miss_df = pd.DataFrame(col_pct_miss, columns = ['column_name','% of Missing']).sort_values(by = '% of Missing', ascending = False)\ncol_pct_miss_df"}, {'role': 'assistant', 'content': 'data_preprocessing'}]