lindong28 commented on a change in pull request #28: URL: https://github.com/apache/flink-ml/pull/28#discussion_r761597164
########## File path: flink-ml-core/src/main/java/org/apache/flink/ml/common/datastream/DataStreamUtils.java ########## @@ -0,0 +1,243 @@ +/* + * Licensed to the Apache Software Foundation (ASF) under one + * or more contributor license agreements. See the NOTICE file + * distributed with this work for additional information + * regarding copyright ownership. The ASF licenses this file + * to you under the Apache License, Version 2.0 (the + * "License"); you may not use this file except in compliance + * with the License. You may obtain a copy of the License at + * + * http://www.apache.org/licenses/LICENSE-2.0 + * + * Unless required by applicable law or agreed to in writing, software + * distributed under the License is distributed on an "AS IS" BASIS, + * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. + * See the License for the specific language governing permissions and + * limitations under the License. + */ + +package org.apache.flink.ml.common.datastream; + +import org.apache.flink.api.common.functions.MapPartitionFunction; +import org.apache.flink.api.common.state.ListState; +import org.apache.flink.api.common.state.ListStateDescriptor; +import org.apache.flink.api.common.typeinfo.TypeInformation; +import org.apache.flink.api.common.typeutils.TypeComparator; +import org.apache.flink.api.java.typeutils.TypeExtractor; +import org.apache.flink.runtime.state.StateInitializationContext; +import org.apache.flink.runtime.state.StateSnapshotContext; +import org.apache.flink.streaming.api.datastream.DataStream; +import org.apache.flink.streaming.api.operators.AbstractStreamOperator; +import org.apache.flink.streaming.api.operators.BoundedOneInput; +import org.apache.flink.streaming.api.operators.OneInputStreamOperator; +import org.apache.flink.streaming.api.operators.TimestampedCollector; +import org.apache.flink.streaming.runtime.streamrecord.StreamRecord; + +import org.apache.commons.collections.IteratorUtils; + +import java.util.HashSet; +import java.util.List; +import java.util.Set; + +/** Provides utility functions for {@link DataStream}. */ +public class DataStreamUtils { + /** + * Applies allReduceSum on the input data stream. The input data stream is supposed to contain + * one double array in each partition. The result data stream has the same parallelism as the + * input, where each partition contains one double array that sums all of the double arrays in + * the input data stream. + * + * <p>Note that we throw exception when one of the following two cases happen: + * <li>There exists one partition that contains more than one double array. + * <li>The length of the double array is not consistent among all partitions. + * + * @param input The input data stream. + * @return The result data stream. + */ + public static DataStream<double[]> allReduceSum(DataStream<double[]> input) { + return AllReduceImpl.allReduceSum(input); + } + + /** + * Collects distinct values in a bounded data stream. The parallelism of the output stream is 1. + * + * @param <T> The class type of the input data stream. + * @param input The bounded input data stream. + * @return The result data stream that contains all the distinct values. + */ + public static <T> DataStream<T> distinct(DataStream<T> input) { + return input.transform( + "distinctInEachPartition", + input.getType(), + new DistinctPartitionOperator<>()) + .setParallelism(input.getParallelism()) + .transform( + "distinctInFinalPartition", + input.getType(), + new DistinctPartitionOperator<>()) + .setParallelism(1); + } + + /** + * Applies a {@link MapPartitionFunction} on a bounded data stream. + * + * @param input The input data stream. + * @param func The user defined mapPartition function. + * @param <IN> The class type of the input element. + * @param <OUT> The class type of output element. + * @return The result data stream. + */ + public static <IN, OUT> DataStream<OUT> mapPartition( + DataStream<IN> input, MapPartitionFunction<IN, OUT> func) { + TypeInformation<OUT> resultType = + TypeExtractor.getMapPartitionReturnTypes(func, input.getType(), null, true); + return input.transform("mapPartition", resultType, new MapPartitionOperator<>(func)) + .setParallelism(input.getParallelism()); + } + + /** + * Sorts the elements in each partition of the input bounded data stream. + * + * @param input The input data stream. + * @param comparator The comparator used to sort the elements. + * @param <IN> The class type of input element. + * @return The sorted data stream. + */ + public static <IN> DataStream<IN> sortPartition( + DataStream<IN> input, TypeComparator<IN> comparator) { + return input.transform( + "sortPartition", input.getType(), new SortPartitionOperator<>(comparator)) + .setParallelism(input.getParallelism()); + } + + /** + * A stream operator to compute the distinct values in each partition of the input bounded data + * stream. + */ + private static class DistinctPartitionOperator<T> extends AbstractStreamOperator<T> + implements OneInputStreamOperator<T, T>, BoundedOneInput { Review comment: I think `BoundedOneInput ` could still be useful when the operator does not extend `AbstractStreamOperator`. 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