code: def rowiter(self):
      # supply data by grouping on the first parameter
      for name, group in self.df.groupby(self.group_by[0]):
          # if there are only three columns (param1, param2, data),
          # then ['data'].values will return the values for a fixed param1
          # in increasing param2 order
          if len(self.params) == 2:
              yield name, group["data"].values
          # if there are more than one params, then we have to do a second
          # group_by, so the values are grouped together for a fixed
          # (param1, param2) combination
          else:
              values = [
                  df_sub["data"].values
                  for _, df_sub in group.groupby(self.group_by[1])
              ]
              yield name, values
  
file_path: sklearn-evaluation/src/sklearn_evaluation/plot/matplotlib/data_grid.py
imports: import numpy
  import pandas
label_desc: Use image node_id 3 for calling the DataGrid obj's underlying member method code with example usage: obj.rowiter() without return types