@Override
  public InternalAggregation buildAggregation(long owningBucketOrdinal) {
    assert owningBucketOrdinal == 0;
    List<InternalHistogram.Bucket> buckets =
        new ArrayList<InternalHistogram.Bucket>((int) bucketOrds.size());
    for (long i = 0; i < bucketOrds.capacity(); ++i) {
      final long ord = bucketOrds.id(i);
      if (ord < 0) {
        continue; // slot is not allocated
      }
      buckets.add(
          histogramFactory.createBucket(
              rounding.valueForKey(bucketOrds.key(i)),
              bucketDocCount(ord),
              bucketAggregations(ord),
              valuesSource.formatter()));
    }

    CollectionUtil.introSort(buckets, order.comparator());

    // value source will be null for unmapped fields
    ValueFormatter formatter = valuesSource != null ? valuesSource.formatter() : null;
    InternalHistogram.EmptyBucketInfo emptyBucketInfo =
        minDocCount == 0
            ? new InternalHistogram.EmptyBucketInfo(rounding, buildEmptySubAggregations())
            : null;
    return histogramFactory.create(
        name, buckets, order, minDocCount, emptyBucketInfo, formatter, keyed);
  }
  @Override
  public void collect(int doc, long owningBucketOrdinal) throws IOException {
    assert owningBucketOrdinal == 0;
    final int valuesCount = values.setDocument(doc);

    long previousKey = Long.MIN_VALUE;
    for (int i = 0; i < valuesCount; ++i) {
      long value = values.nextValue();
      long key = rounding.roundKey(value);
      assert key >= previousKey;
      if (key == previousKey) {
        continue;
      }
      long bucketOrd = bucketOrds.add(key);
      if (bucketOrd < 0) { // already seen
        bucketOrd = -1 - bucketOrd;
      }
      collectBucket(doc, bucketOrd);
      previousKey = key;
    }
  }