code: def grouped_mappings(self,id):
          
          g = self.get_xref_graph()
          m = {}
          for n in g.neighbors(id):
              [prefix, local] = n.split(':')
              if prefix not in m:
                  m[prefix] = []
              m[prefix].append(n)
          return m
docs: return all mappings for a node, grouped by ID prefix