Matrix of String with rows of different lenght; stores the name of the categories
(each row corresponds to a different feature); meaningful for categorical features only.
Classify a single instance, writing the computed probabilities at position InstanceIdx
of probabilities, and the predicted class at position InstanceIdx of predictions
Counts that correspond to counts-after-dropping-missing for MarFeatures,
bivariate count: frequency are computed for each output class and for each class of the
feature.