When I use Classify on a dataset with inputs that are matrices with different row sizes (i.e., sequences), and I check the internals of the ClassifierFunction by running
c[], I see that Mathematica automatically applies some preprocessor that is called NumericalSequenceExtractFeatures. I hovered over it to see what it is doing, but it is unclear to me what kind of feature extraction it is performing. I was wondering what exactly does it do? See the attached image for a screenshot of what I am talking about.
The input type that Mathematica assigns to my dataset is NumericalVectorSequence, and it seems that this preprocessing step is done whenever you have a dataset of vector sequences, where the sequence length is not constant.