code: def get_merged_pianoroll(self, mode='sum'):
          
          stacked = self.get_stacked_pianoroll()
  
          if mode == 'any':
              merged = np.any(stacked, axis=2)
          elif mode == 'sum':
              merged = np.sum(stacked, axis=2)
          elif mode == 'max':
              merged = np.max(stacked, axis=2)
          else:
              raise ValueError("`mode` must be one of {'max', 'sum', 'any'}.")
  
          return merged
docs: Return the merged pianoroll.
  
          Parameters
          ----------
          mode : {'sum', 'max', 'any'}
              A string that indicates the merging strategy to apply along the
              track axis. Default to 'sum'.
  
              - In 'sum' mode, the merged pianoroll is the sum of all the
                pianorolls. Note that for binarized pianorolls, integer summation
                is performed.
              - In 'max' mode, for each pixel, the maximum value among all the
                pianorolls is assigned to the merged pianoroll.
              - In 'any' mode, the value of a pixel in the merged pianoroll is
                True if any of the pianorolls has nonzero value at that pixel;
                False if all pianorolls are inactive (zero-valued) at that pixel.
  
          Returns
          -------
          merged : np.ndarray, shape=(n_time_steps, 128)
              The merged pianoroll.