Creating a model per category

Generates models for a dataset, simulating a root split on a given field.

• Given an input dataset and one of its categorical fields, create a dataset for each field category.

For each category dataset, create a model of the given kind.

If the provided field has missing values in the input dataset, a model for instances with missing as their "category" will also be created.

• Return a map with the list of datasets, models and categories for use during predictions.

The lists are returned in a map as the execution's result, for later convenience, as well as in the output named "result".