docs: def map_indices_child2parent(child, child_indices):
      """Map child RTDCBase event indices to parent RTDCBase
  
      Parameters
      ----------
      child: RTDC_Hierarchy
          hierarchy child with `child_indices`
      child_indices: 1d ndarray
          child indices to map
  
      Returns
      -------
      parent_indices: 1d ndarray
          hierarchy parent indices
      """
      parent = child.hparent
      # filters
      pf = parent.filter.all
      # indices corresponding to all child events
      idx = np.where(pf)[0]  # True means present in the child
      # indices corresponding to selected child events
      parent_indices = idx[child_indices]
      return parent_indices