code: def _drop_duplicate_ij(self):
          
          self.network['ij'] = list(map(lambda x: tuple(sorted(x)), list(
              zip(*[self.network['i'].values, self.network['j'].values]))))
          self.network.drop_duplicates(['ij', 't'], inplace=True)
          self.network.reset_index(inplace=True, drop=True)
          self.network.drop('ij', inplace=True, axis=1)
docs: Drops duplicate entries from the network dataframe.