org.apache.flink.api.java.functions.SampleInPartition Maven / Gradle / Ivy
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package org.apache.flink.api.java.functions;
import org.apache.flink.annotation.Internal;
import org.apache.flink.api.common.functions.RichMapPartitionFunction;
import org.apache.flink.api.java.sampling.DistributedRandomSampler;
import org.apache.flink.api.java.sampling.IntermediateSampleData;
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;
/**
* SampleInPartition wraps the sample logic on the partition side (the first phase of distributed
* sample algorithm). It executes the partition side sample logic in a mapPartition function.
*
* @param The type of input data
*/
@Internal
public class SampleInPartition extends RichMapPartitionFunction> {
private boolean withReplacement;
private int numSample;
private long seed;
/**
* Create a function instance of SampleInPartition.
*
* @param withReplacement Whether element can be selected more than once.
* @param numSample Fixed sample size.
* @param seed Random generator seed.
*/
public SampleInPartition(boolean withReplacement, int numSample, long seed) {
this.withReplacement = withReplacement;
this.numSample = numSample;
this.seed = seed;
}
@Override
public void mapPartition(Iterable values, Collector> out) throws Exception {
DistributedRandomSampler sampler;
long seedAndIndex = seed + getRuntimeContext().getIndexOfThisSubtask();
if (withReplacement) {
sampler = new ReservoirSamplerWithReplacement(numSample, seedAndIndex);
} else {
sampler = new ReservoirSamplerWithoutReplacement(numSample, seedAndIndex);
}
Iterator> sampled = sampler.sampleInPartition(values.iterator());
while (sampled.hasNext()) {
out.collect(sampled.next());
}
}
}