Separated Bit Plan encoder fit / transform behaves un-intuitively

[lucgiffon]

Hello,

In the scikit-learn framework, I believe the fit / transform methods are coded with the following philosophy:

• fit changes the state of the "transforming" object but not that of the input
• transform doesn't change the state of the "transforming" object but the input
• fit_transform changes both the "transforming" object and the input

Or at least this is how I see things.

But objects of the SeparatedBitPlanEncoder class from the lightonml library doesn't behave like this. Instances of this class change their inner state when we call their transform method. I find this misleading because it makes no difference between the transform method and the fit_transform one.

The consequence is that we cannot instanciate one SeparatedBitPlanEncoder and one SeparatedBitPlanDecoder once and for all and then use the same for all the OPU calls ! I can see from here the huge problems such a thing could cause !!!

At the very least, the transform method of SeparatedBitPlanEncoder should be disabled and only fit_transform should remains. This way, it would be clear that we change its state when using it. But an even better improvement would be to have a real fit method that actually fits to its input and then a transform method that would raise an exception if the input values are out of the range of values it is capable to handle.

I really need this feature so I am going to implement it for myself. If you want, I can make a PR when it is done.

Bye

[iacolippo]

Hello Luc, a PR would certainly be welcome!