code: def group_bar(self, column_label, **vargs):
          
          self.group(column_label).bar(column_label, **vargs)
docs: Plot a bar chart for the table.
  
          The values of the specified column are grouped and counted, and one
          bar is produced for each group.
  
          Note: This differs from ``bar`` in that there is no need to specify
          bar heights; the height of a category's bar is the number of copies
          of that category in the given column.  This method behaves more like
          ``hist`` in that regard, while ``bar`` behaves more like ``plot`` or
          ``scatter`` (which require the height of each point to be specified).
  
          Args:
              ``column_label`` (str or int): The name or index of a column
  
          Kwargs:
              overlay (bool): create a chart with one color per data column;
                  if False, each will be displayed separately.
  
              width (float): The width of the plot, in inches
              height (float): The height of the plot, in inches
  
              vargs: Additional arguments that get passed into `plt.bar`.
                  See http://matplotlib.org/api/pyplot_api.html#matplotlib.pyplot.bar
                  for additional arguments that can be passed into vargs.