HashingEncoder does not accept handle_unknown argument

[janmotl]

Can HashingEncoder accept new values (values that are not observed in the training set) in the testing dataset?

If yes, it should possibly be noted in the documentation of the encoder.

[wdm0006]

Yes, it can. Agreed on documentation, it behaves differently than many of the other encoders in that it does not maintain a dictionary of potential categories, you can throw whatever you want at it.

[janmotl]

Documentation extended with b418a2a