docs: public List<Triple<F,L,Double>> getTopFeatures(Set<L> labels,
                                                   double threshold, boolean useMagnitude, int numFeatures,
                                                   boolean descending)
    {
      if (labels != null) {
        Set<Integer> iLabels = getLabelIndices(labels);
        return getTopFeaturesLabelIndices(iLabels, threshold, useMagnitude, numFeatures, descending);
      } else {
        return getTopFeaturesLabelIndices(null, threshold, useMagnitude, numFeatures, descending);
      }
    }