docs: def count_by_type(self):
          """Count how many times each individual salt bridge occured throughout the simulation.
          Returns numpy array."""
          saltbridges = defaultdict(int)
          for contact in self.timeseries:
              #count by residue name not by proteinring
              pkey = (contact.ligandatomid,contact.ligandatomname, contact.resid,contact.resname,contact.segid)
              saltbridges[pkey]+=1
          dtype = [("ligand_atom_id",int),("ligand_atom_name","|U4"),("resid",int),("resname","|U4"),("segid","|U8"),("frequency",float) ]
          out = np.empty((len(saltbridges),),dtype=dtype)
          tsteps = float(len(self.timesteps))
          for cursor,(key,count) in enumerate(saltbridges.iteritems()):
              out[cursor] = key + (count / tsteps,)
          return out.view(np.recarray)