aruggero commented on code in PR #3418: URL: https://github.com/apache/solr/pull/3418#discussion_r2282280820
########## solr/core/src/java/org/apache/solr/search/combine/ReciprocalRankFusion.java: ########## @@ -0,0 +1,252 @@ +/* + * 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.combine; + +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 org.apache.lucene.document.Document; +import org.apache.lucene.search.Explanation; +import org.apache.lucene.search.Query; +import org.apache.lucene.search.TotalHits; +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.handler.component.ShardDoc; +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.SolrDocumentFetcher; +import org.apache.solr.search.SolrIndexSearcher; +import org.apache.solr.search.SortedIntDocSet; + +/** + * The ReciprocalRankFusion class implements a query and response combiner that uses the Reciprocal + * Rank Fusion (RRF) algorithm to combine multiple ranked lists into a single ranked list. + */ +public class ReciprocalRankFusion extends QueryAndResponseCombiner { + + private int k; + + public int getK() { + return k; + } + + public ReciprocalRankFusion() { + this.k = CombinerParams.COMBINER_RRF_K_DEFAULT; + } + + @Override + public void init(NamedList<?> args) { + Object kParam = args.get("k"); + if (kParam != null) { + this.k = Integer.parseInt(kParam.toString()); + } + } + + @Override + public QueryResult combine(List<QueryResult> rankedLists, SolrParams solrParams) { + int kVal = solrParams.getInt(CombinerParams.COMBINER_RRF_K, this.k); + List<DocList> docLists = getDocListsFromQueryResults(rankedLists); + QueryResult combinedResult = new QueryResult(); + combineResults(combinedResult, docLists, false, kVal); + return combinedResult; + } + + private static List<DocList> getDocListsFromQueryResults(List<QueryResult> rankedLists) { + List<DocList> docLists = new ArrayList<>(rankedLists.size()); + for (QueryResult rankedList : rankedLists) { + docLists.add(rankedList.getDocList()); + } + return docLists; + } + + @Override + public List<ShardDoc> combine(Map<String, List<ShardDoc>> shardDocMap, SolrParams solrParams) { + int kVal = solrParams.getInt(CombinerParams.COMBINER_RRF_K, this.k); + HashMap<String, Float> docIdToScore = new HashMap<>(); + Map<String, ShardDoc> docIdToShardDoc = new HashMap<>(); + List<ShardDoc> finalShardDocList = new ArrayList<>(); + for (Map.Entry<String, List<ShardDoc>> shardDocEntry : shardDocMap.entrySet()) { + List<ShardDoc> shardDocList = shardDocEntry.getValue(); + int ranking = 1; + while (ranking <= shardDocList.size()) { + String docId = shardDocList.get(ranking - 1).id.toString(); + docIdToShardDoc.put(docId, shardDocList.get(ranking - 1)); + float rrfScore = 1f / (kVal + ranking); + docIdToScore.compute(docId, (id, score) -> (score == null) ? rrfScore : score + rrfScore); + ranking++; + } + } + List<Map.Entry<String, Float>> sortedByScoreDescending = + docIdToScore.entrySet().stream() + .sorted(Collections.reverseOrder(Map.Entry.comparingByValue())) + .toList(); + for (Map.Entry<String, Float> scoredDoc : sortedByScoreDescending) { + String docId = scoredDoc.getKey(); + Float score = scoredDoc.getValue(); + ShardDoc shardDoc = docIdToShardDoc.get(docId); + shardDoc.score = score; + finalShardDocList.add(shardDoc); + } + return finalShardDocList; + } + + private Map<Integer, Integer[]> combineResults( + QueryResult combinedRankedList, + List<DocList> rankedLists, + boolean saveRankPositionsForExplain, + int kVal) { + Map<Integer, Integer[]> docIdToRanks = null; + HashMap<Integer, Float> docIdToScore = new HashMap<>(); + long totalMatches = 0; + for (DocList rankedList : rankedLists) { + DocIterator docs = rankedList.iterator(); + totalMatches = Math.max(totalMatches, rankedList.matches()); Review Comment: @ercsonusharma could you explain to me what totalMatches represents and why it is computed in this way? -- This is an automated message from the Apache Git Service. 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