docs: public static <T> T quantile(List<? extends T> data, Comparator<? super T> comparator, int begin, int end, double quant) {
      final int length = end - begin;
      assert (length > 0) : "Quantile on empty set?";
      // Integer division is "floor" since we are non-negative.
      final double dleft = begin + (length - 1) * quant;
      final int ileft = (int) Math.floor(dleft);
  
      quickSelect(data, comparator, begin, end, ileft);
      return data.get(ileft);
    }