docs: public void incrementFeatureByIndex(double amount, int... key) {
      if (isDense) {
        statistics.incrementEntry(amount, key);
      } else {
        Tensor increment = SparseTensor.singleElement(getTensorDimensions(), getTensorSizes(),
            key, amount);
        statisticsTensor = statisticsTensor.elementwiseAddition(increment);
      }
    }