code: def colnames(self):
      values = self.df[self.group_by[1]].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 5 for calling the DataGrid obj's underlying member method code with example usage: obj.colnames() and returns: values