code: def add_group_mindist(self, group_definitions, group_pairs='all', threshold=None, periodic=True):
          r
          from .distances import GroupMinDistanceFeature
          # Some thorough input checking and reformatting
          group_definitions, group_pairs, distance_list, group_identifiers = \
              _parse_groupwise_input(group_definitions, group_pairs, self.logger, 'add_group_mindist')
          distance_list = self._check_indices(distance_list)
  
          f = GroupMinDistanceFeature(self.topology, group_definitions, group_pairs, distance_list, group_identifiers, threshold, periodic)
          self.__add_feature(f)
docs: r"""
          Adds the minimum distance between groups of atoms to the feature list. If the groups of
          atoms are identical to residues, use :py:obj:`add_residue_mindist <pyemma.coordinates.data.featurizer.MDFeaturizer.add_residue_mindist>`.
  
          Parameters
          ----------
  
          group_definitions : list of 1D-arrays/iterables containing the group definitions via atom indices.
              If there is only one group_definition, it is assumed the minimum distance within this group (excluding the
              self-distance) is wanted. In this case, :py:obj:`group_pairs` is ignored.
  
          group_pairs :  Can be of two types:
              'all'
                  Computes minimum distances between all pairs of groups contained in the group definitions
  
              ndarray((n, 2), dtype=int):
                  n x 2 array with the pairs of groups for which the minimum distances will be computed.
  
          threshold : float, optional, default is None
              distances below this threshold (in nm) will result in a feature 1.0, distances above will result in 0.0. If
              left to None, the numerical value will be returned
  
          periodic : bool, optional, default = True
              If `periodic` is True and the trajectory contains unitcell
              information, we will treat dihedrals that cross periodic images
              using the minimum image convention.