package org.apache.lucene.facet.sampling;
import java.io.IOException;
import java.util.Random;
import org.apache.lucene.facet.old.ScoredDocIDs;
import org.apache.lucene.facet.old.ScoredDocIDsIterator;
import org.apache.lucene.facet.old.ScoredDocIdsUtils;
/*
* 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.
*/
/**
* Simple random sampler
*/
public class RandomSampler extends Sampler {
private final Random random;
public RandomSampler() {
super();
this.random = new Random();
}
public RandomSampler(SamplingParams params, Random random) throws IllegalArgumentException {
super(params);
this.random = random;
}
@Override
protected SampleResult createSample(ScoredDocIDs docids, int actualSize, int sampleSetSize) throws IOException {
final int[] sample = new int[sampleSetSize];
final int maxStep = (actualSize * 2 ) / sampleSetSize; //floor
int remaining = actualSize;
ScoredDocIDsIterator it = docids.iterator();
int i = 0;
// select sample docs with random skipStep, make sure to leave sufficient #docs for selection after last skip
while (i<sample.length && remaining>(sampleSetSize-maxStep-i)) {
int skipStep = 1 + random.nextInt(maxStep);
// Skip over 'skipStep' documents
for (int j=0; j<skipStep; j++) {
it.next();
-- remaining;
}
sample[i++] = it.getDocID();
}
// Add leftover documents to the sample set
while (i<sample.length) {
it.next();
sample[i++] = it.getDocID();
}
ScoredDocIDs sampleRes = ScoredDocIdsUtils.createScoredDocIDsSubset(docids, sample);
SampleResult res = new SampleResult(sampleRes, sampleSetSize/(double)actualSize);
return res;
}
}