TDigest Combiner

TDigestFn.java

static class TDigestFn extends Combine.CombineFn<Double, TDigest, TDigest> {
    private static final int COMPRESSION_RATIO = 100;

    @Override
    public TDigest createAccumulator() {
      return TDigest.createDigest(COMPRESSION_RATIO);
    }

    @Override
    public TDigest addInput(TDigest tDigest, Double value) {
      tDigest.add(value);
      return tDigest;
    }

    @Override
    public TDigest mergeAccumulators(Iterable<TDigest> iterable) {
      final TDigest mergedDigest = TDigest.createDigest(COMPRESSION_RATIO);
      for (TDigest digest : iterable) {
        mergedDigest.add(digest);
      }
      return mergedDigest;
    }

    @Override
    public TDigest extractOutput(TDigest tDigest) {
      return tDigest;
    }
  }