docs: public int getFeatureCount(Set<L> labels, double threshold, boolean useMagnitude)
    {
      if (labels != null) {
        Set<Integer> iLabels = getLabelIndices(labels);
        return getFeatureCountLabelIndices(iLabels, threshold, useMagnitude);
      } else {
        return getFeatureCount(threshold, useMagnitude);
      }
    }