yunfengzhou-hub commented on code in PR #97: URL: https://github.com/apache/flink-ml/pull/97#discussion_r888730986
########## flink-ml-core/src/main/java/org/apache/flink/ml/common/datastream/DataStreamUtils.java: ########## @@ -182,4 +307,79 @@ public void snapshotState(StateSnapshotContext context) throws Exception { } } } + + /** + * A stream operator that takes a randomly sampled subset of elements in a bounded data stream. + */ + private static class SamplingOperator<T> extends AbstractStreamOperator<List<T>> + implements OneInputStreamOperator<T, List<T>>, BoundedOneInput { + private final int numSamples; + + private final Random random; + + private ListState<T> samplesState; + + private List<T> samples; + + private ListState<Integer> countState; + + private int count; + + SamplingOperator(int numSamples, long randomSeed) { + this.numSamples = numSamples; + this.random = new Random(randomSeed); + } + + @Override + public void initializeState(StateInitializationContext context) throws Exception { + super.initializeState(context); + + ListStateDescriptor<T> samplesDescriptor = + new ListStateDescriptor<>( + "samplesState", + getOperatorConfig() + .getTypeSerializerIn(0, getClass().getClassLoader())); + samplesState = context.getOperatorStateStore().getListState(samplesDescriptor); + samples = new ArrayList<>(); + samplesState.get().forEach(samples::add); + + ListStateDescriptor<Integer> countDescriptor = + new ListStateDescriptor<>("countState", IntSerializer.INSTANCE); + countState = context.getOperatorStateStore().getListState(countDescriptor); + Iterator<Integer> countIterator = countState.get().iterator(); + if (countIterator.hasNext()) { + count = countIterator.next(); + } else { + count = 0; + } + } + + @Override + public void snapshotState(StateSnapshotContext context) throws Exception { + super.snapshotState(context); + samplesState.update(samples); + countState.update(Collections.singletonList(count)); + } + + @Override + public void processElement(StreamRecord<T> streamRecord) throws Exception { + T sample = streamRecord.getValue(); + count++; + + // Code below is inspired by the Reservoir Sampling algorithm. + if (samples.size() < numSamples) { + samples.add(sample); + } else { + if (random.nextInt(count) < numSamples) { + samples.set(random.nextInt(numSamples), sample); + } + } + } + + @Override + public void endInput() throws Exception { + Collections.shuffle(samples, random); Review Comment: I think it is necessary. Otherwise the first arriving element, if sampled, will always be the first returning element, while elements that arrived after the first sampled `numSamples` elements will be returned in random order. -- This is an automated message from the Apache Git Service. To respond to the message, please log on to GitHub and use the URL above to go to the specific comment. To unsubscribe, e-mail: issues-unsubscr...@flink.apache.org For queries about this service, please contact Infrastructure at: us...@infra.apache.org