Data Manipulation of categorical data in the background in ML process

Hi everybody,

I have a question regarding KNIME’s data manipulation in the machine learning process.

In KNIME it is possible to put categorical data as a column (i.e. as a string) in a ML model, without a manual preprocessing step.

I am interested in what is KNIME doing with these data in the background? Are they doing a numeric transformation or an one-hot encoding?

The following models are relevant:

XGBoost Tree Ensemble Learner

RandomForest Learner

Gradient Boosted Trees Learner

H2O Gradient Boosting Machine Learner

H2O Random Forest Learner

I would really appreciate an answer to this topic.