code: def rownames(self):
      values = self.df[self.group_by[0]].unique()
      values.sort()
      return values
  
file_path: sklearn-evaluation/src/sklearn_evaluation/plot/matplotlib/data_grid.py
imports: import numpy
  import pandas
label_desc: Use image node_id 4 for calling the DataGrid obj's underlying member method code with example usage: obj.rownames() and returns: values