/*
* 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.api.java.functions;
import org.apache.flink.annotation.Internal;
import org.apache.flink.api.common.functions.GroupReduceFunction;
import org.apache.flink.api.java.sampling.IntermediateSampleData;
import org.apache.flink.api.java.sampling.DistributedRandomSampler;
import org.apache.flink.api.java.sampling.ReservoirSamplerWithReplacement;
import org.apache.flink.api.java.sampling.ReservoirSamplerWithoutReplacement;
import org.apache.flink.util.Collector;
import java.util.Iterator;
/**
* SampleInCoordinator wraps the sample logic of the coordinator side (the second phase of
* distributed sample algorithm). It executes the coordinator side sample logic in an all reduce
* function. The user needs to make sure that the operator parallelism of this function is 1 to
* make sure this is a central coordinator. Besides, we do not need the task index information for
* random generator seed as the parallelism must be 1.
*
* @param <T> the data type wrapped in ElementWithRandom as input.
*/
@Internal
public class SampleInCoordinator<T> implements GroupReduceFunction<IntermediateSampleData<T>, T> {
private boolean withReplacement;
private int numSample;
private long seed;
/**
* Create a function instance of SampleInCoordinator.
*
* @param withReplacement Whether element can be selected more than once.
* @param numSample Fixed sample size.
* @param seed Random generator seed.
*/
public SampleInCoordinator(boolean withReplacement, int numSample, long seed) {
this.withReplacement = withReplacement;
this.numSample = numSample;
this.seed = seed;
}
@Override
public void reduce(Iterable<IntermediateSampleData<T>> values, Collector<T> out) throws Exception {
DistributedRandomSampler<T> sampler;
if (withReplacement) {
sampler = new ReservoirSamplerWithReplacement<>(numSample, seed);
} else {
sampler = new ReservoirSamplerWithoutReplacement<>(numSample, seed);
}
Iterator<T> sampled = sampler.sampleInCoordinator(values.iterator());
while (sampled.hasNext()) {
out.collect(sampled.next());
}
}
}