How to use

compact

method

in

org.apache.beam.sdk.transforms.Combine$CombineFn

 @FinishBundle
 public void outputAccumulators(FinishBundleContext context) {
  for (Map.Entry<WindowedStructuralKey<K>, AccumT> preCombineEntry : accumulators.entrySet()) {
   context.output(
     KV.of(preCombineEntry.getKey().getKey(), combineFn.compact(preCombineEntry.getValue())),
     timestamps.get(preCombineEntry.getKey()),
     preCombineEntry.getKey().getWindow());
  }
  accumulators = null;
  timestamps = null;
 }
}

@Override
public Object[] compact(Object[] accumulator) {
 for (int i = 0; i < combineFnCount; ++i) {
  accumulator[i] = combineFns.get(i).compact(accumulator[i]);
 }
 return accumulator;
}

private static <InputT, AccumT, OutputT> List<AccumT> combineInputs(
  CombineFn<InputT, AccumT, OutputT> fn, Iterable<? extends Iterable<InputT>> shards) {
 List<AccumT> accumulators = new ArrayList<>();
 int maybeCompact = 0;
 for (Iterable<InputT> shard : shards) {
  AccumT accumulator = fn.createAccumulator();
  for (InputT elem : shard) {
   accumulator = fn.addInput(accumulator, elem);
  }
  if (maybeCompact++ % 2 == 0) {
   accumulator = fn.compact(accumulator);
  }
  accumulators.add(accumulator);
 }
 return accumulators;
}

@Override
public AccumT compact(AccumT accumulator, Context c) {
 return combineFn.compact(accumulator);
}

 @Override
 public AccumT compact(
   AccumT accumulator,
   PipelineOptions options,
   SideInputReader sideInputReader,
   Collection<? extends BoundedWindow> windows) {
  return combineFn.compact(accumulator);
 }
}

@Override
public AccumT compact(AccumT accumulator) {
 return fn.compact(accumulator);
}

@Override
public AccumT compact(AccumT accumulator) {
 return fn.compact(accumulator);
}