1 package org.apache.lucene.facet.search.sampling;
3 import java.io.IOException;
4 import java.util.Random;
6 import org.apache.lucene.facet.search.ScoredDocIDs;
7 import org.apache.lucene.facet.search.ScoredDocIDsIterator;
8 import org.apache.lucene.facet.util.ScoredDocIdsUtils;
11 * Licensed to the Apache Software Foundation (ASF) under one or more
12 * contributor license agreements. See the NOTICE file distributed with
13 * this work for additional information regarding copyright ownership.
14 * The ASF licenses this file to You under the Apache License, Version 2.0
15 * (the "License"); you may not use this file except in compliance with
16 * the License. You may obtain a copy of the License at
18 * http://www.apache.org/licenses/LICENSE-2.0
20 * Unless required by applicable law or agreed to in writing, software
21 * distributed under the License is distributed on an "AS IS" BASIS,
22 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
23 * See the License for the specific language governing permissions and
24 * limitations under the License.
28 * Simple random sampler
30 public class RandomSampler extends Sampler {
32 private final Random random;
34 public RandomSampler() {
36 this.random = new Random();
39 public RandomSampler(SamplingParams params, Random random) throws IllegalArgumentException {
45 protected SampleResult createSample(ScoredDocIDs docids, int actualSize, int sampleSetSize) throws IOException {
46 final int[] sample = new int[sampleSetSize];
47 final int maxStep = (actualSize * 2 ) / sampleSetSize; //floor
48 int remaining = actualSize;
49 ScoredDocIDsIterator it = docids.iterator();
51 // select sample docs with random skipStep, make sure to leave sufficient #docs for selection after last skip
52 while (i<sample.length && remaining>(sampleSetSize-maxStep-i)) {
53 int skipStep = 1 + random.nextInt(maxStep);
54 // Skip over 'skipStep' documents
55 for (int j=0; j<skipStep; j++) {
59 sample[i++] = it.getDocID();
61 // Add leftover documents to the sample set
62 while (i<sample.length) {
64 sample[i++] = it.getDocID();
66 ScoredDocIDs sampleRes = ScoredDocIdsUtils.createScoredDocIDsSubset(docids, sample);
67 SampleResult res = new SampleResult(sampleRes, sampleSetSize/(double)actualSize);