code: def reindex(self):
          
          _map = dict(zip(self.micro_indices, reindex(self.micro_indices)))
          partition = tuple(
              tuple(_map[index] for index in group)
              for group in self.partition
          )
          return CoarseGrain(partition, self.grouping)
docs: Re-index this coarse graining to use squeezed indices.
  
          The output grouping is translated to use indices ``0..n``, where ``n``
          is the number of micro indices in the coarse-graining. Re-indexing does
          not effect the state grouping, which is already index-independent.
  
          Returns:
              CoarseGrain: A new |CoarseGrain| object, indexed from ``0..n``.
  
          Example:
              >>> partition = ((1, 2),)
              >>> grouping = (((0,), (1, 2)),)
              >>> coarse_grain = CoarseGrain(partition, grouping)
              >>> coarse_grain.reindex()
              CoarseGrain(partition=((0, 1),), grouping=(((0,), (1, 2)),))