Support for transformer-only pipelines

[vruusmann]

Based on jpmml/jpmml-sklearn#86

At the moment it's impossible to generate transformer-only pipelines, because the ModelEncoder#encodePMML(Model) method applies a set of visitors that clean the soon-to-be-generated PMML document from all unused preprocessing instructions:
https://github.com/jpmml/jpmml-converter/blob/master/src/main/java/org/jpmml/converter/ModelEncoder.java#L53-L56

Possible solution: class ModelEncoder should provide a "transformer-only" conversion mode.

[vruusmann]

Related to jpmml/jpmml-evaluator#96

In other words, there should be an API for producing transformer-only PMML documents, and then consuming them.

[wunderbarr]

Hello,
When could we expect this "transformer-only" conversion mode?
And our team is looking forward to this mode :)
Moreover, if it is possible, a full example could be provided first before this mode, e.g for PCA.
Because I am not familiar with PMML file, it is difficult and confusing for me to adjust relevant configuration as your suggestion in Support for transformer-only pipelines.
Thank you!

[sin-en-2009]

Hello,
When could we expect this "transformer-only" conversion mode?
And my team is looking forward to this mode :)
I am not familiar with PMML file, it is difficult and confusing for me to adjust relevant configuration as your suggestion in Support for transformer-only pipelines.
And how do I look at the results of the data transformation, which is what the data looks like before I put it into the evaluator?
Thank you!