docs: protected List<Centroid> computeCentroids(int dim, List<V> vectorcolumn, List<ClassLabel> keys, Map<ClassLabel, IntList> classes) {
      final int numc = keys.size();
      List<Centroid> centroids = new ArrayList<>(numc);
      for(int i = 0; i < numc; i++) {
        Centroid c = new Centroid(dim);
        for(IntIterator it = classes.get(keys.get(i)).iterator(); it.hasNext();) {
          c.put(vectorcolumn.get(it.nextInt()));
        }
        centroids.add(c);
      }
      return centroids;
    }