code: public void add(ScalableStatistics other) {
      count += other.count;
      min = Math.min(min, other.min);
      max = Math.max(max, other.max);
      sum += other.sum;
      sumOfSquares += other.sumOfSquares;
      tdigest.add(other.tdigest);
      if (other.exactValues != null) {
        for (int i = 0; i < other.numExactValues; i++) {
          addQuantileValue(other.exactValues[i]);
        }
      }
    }
docs: Merges another statistics instance into this instance. For example, this way the independent
  stats and quantiles of each separate MapReduce task can be merged into a single overall job
  summary statistic.