renatoh commented on code in PR #2489: URL: https://github.com/apache/solr/pull/2489#discussion_r1624657341
########## solr/core/src/java/org/apache/solr/search/combining/ReciprocalRankFusion.java: ########## @@ -0,0 +1,208 @@ +/* + * 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.solr.search.combining; + +import static org.apache.lucene.search.TotalHits.Relation.GREATER_THAN_OR_EQUAL_TO; + +import java.io.IOException; +import java.util.ArrayList; +import java.util.Collections; +import java.util.HashMap; +import java.util.List; +import java.util.Map; +import java.util.StringJoiner; +import java.util.stream.Collectors; +import java.util.stream.Stream; +import org.apache.lucene.document.Document; +import org.apache.lucene.search.Explanation; +import org.apache.lucene.search.Query; +import org.apache.solr.common.params.CombinerParams; +import org.apache.solr.common.params.SolrParams; +import org.apache.solr.common.util.NamedList; +import org.apache.solr.common.util.SimpleOrderedMap; +import org.apache.solr.schema.IndexSchema; +import org.apache.solr.search.DocIterator; +import org.apache.solr.search.DocList; +import org.apache.solr.search.DocSlice; +import org.apache.solr.search.QueryResult; +import org.apache.solr.search.SolrIndexSearcher; +import org.apache.solr.search.SortedIntDocSet; + +/** + * Reciprocal Rank Fusion (RRF) is an algorithm that takes in input multiple ranked lists to produce + * a unified result set. Examples of use cases where RRF can be used include hybrid search and + * multiple Knn vector queries executed concurrently. RRF is based on the concept of reciprocal + * rank, which is the inverse of the rank of a document in a ranked list of search results. The + * combination of search results happens taking into account the position of the items in the + * original rankings, and giving higher score to items that are ranked higher in multiple lists. RRF + * was introduced the first time by Cormack et al. in [1].<br> + * + * <p>[1] Cormack, Gordon V. et al. “Reciprocal rank fusion outperforms condorcet and individual + * rank learning methods.” Proceedings of the 32nd international ACM SIGIR conference on Research + * and development in information retrieval (2009)<br> + */ +public class ReciprocalRankFusion extends QueriesCombiner { + int k; + + public ReciprocalRankFusion(SolrParams requestParams) { + super(requestParams); + this.k = + requestParams.getInt(CombinerParams.COMBINER_RRF_K, CombinerParams.COMBINER_RRF_K_DEFAULT); + } + + @Override + public QueryResult combine(QueryResult[] rankedLists) { + QueryResult combinedRankedList = initCombinedResult(rankedLists); + List<DocList> docLists = new ArrayList<>(rankedLists.length); + for (QueryResult rankedList : rankedLists) { + docLists.add(rankedList.getDocList()); + } + combineResults(combinedRankedList, docLists, false); + return combinedRankedList; + } + + private Map<Integer, Integer[]> combineResults( + QueryResult combinedRankedList, + List<DocList> rankedLists, + boolean saveRankPositionsForExplain) { + Map<Integer, Integer[]> docIdToRanks = null; + HashMap<Integer, Float> docIdToScore = new HashMap<>(); + for (DocList rankedList : rankedLists) { + DocIterator docs = rankedList.iterator(); + int ranking = 1; + while (docs.hasNext() && ranking <= upTo) { + int docId = docs.nextDoc(); + float rrfScore = 1f / (k + ranking); + docIdToScore.compute(docId, (id, score) -> (score == null) ? rrfScore : score + rrfScore); + ranking++; + } + } + Stream<Map.Entry<Integer, Float>> sortedByScoreDescending = + docIdToScore.entrySet().stream() + .sorted(Collections.reverseOrder(Map.Entry.comparingByValue())); + + int combinedResultsLength = docIdToScore.size(); + int[] combinedResultsDocIds = new int[combinedResultsLength]; + float[] combinedResultScores = new float[combinedResultsLength]; + + int i = 0; + for (Map.Entry<Integer, Float> scoredDoc : + sortedByScoreDescending.collect(Collectors.toList())) { + combinedResultsDocIds[i] = scoredDoc.getKey(); + combinedResultScores[i] = scoredDoc.getValue(); + i++; + } + + if (saveRankPositionsForExplain) { + docIdToRanks = getRanks(rankedLists, combinedResultsDocIds); + } + + DocSlice combinedResultSlice = + new DocSlice( + 0, + combinedResultsLength, + combinedResultsDocIds, + combinedResultScores, + combinedResultsLength, + combinedResultScores[0], + GREATER_THAN_OR_EQUAL_TO); + combinedRankedList.setDocList(combinedResultSlice); + SortedIntDocSet docSet = new SortedIntDocSet(combinedResultsDocIds, combinedResultsLength); + combinedRankedList.setDocSet(docSet); + + return docIdToRanks; + } + + private Map<Integer, Integer[]> getRanks(List<DocList> docLists, int[] combinedResultsDocIDs) { + Map<Integer, Integer[]> docIdToRanks; + docIdToRanks = new HashMap<>(); + for (int docID : combinedResultsDocIDs) { + docIdToRanks.put(docID, new Integer[docLists.size()]); Review Comment: oh dear, I completely missed the[] and thought you are create a new Integer by doing: new Integer() and therefore preventing them from being cached. sorry, my bad! -- This is an automated message from the Apache Git Service. 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