code: public ConnectedStreams<IN1, IN2> keyBy(KeySelector<IN1, ?> keySelector1, KeySelector<IN2, ?> keySelector2) {
  		return new ConnectedStreams<>(environment, inputStream1.keyBy(keySelector1),
  				inputStream2.keyBy(keySelector2));
  	}
docs: KeyBy operation for connected data stream. Assigns keys to the elements of
  input1 and input2 using keySelector1 and keySelector2.
  
  @param keySelector1
  The {@link KeySelector} used for grouping the first input
  @param keySelector2
  The {@link KeySelector} used for grouping the second input
  @return The partitioned {@link ConnectedStreams}