def return_string(x):
      if [x.a=='s' & x.b=='S' & x.c=='s']
          return 'S'
      else if[x.a=='s' & x.b=='NS' & x.c=='s']
          return 'S'
      else if[x.a=='s' & x.b=='S' & x.c=='NS']
          return 'NS;

func= udf(returnstring,types.StringType())