harenlin commented on code in PR #13470:
URL: https://github.com/apache/lucene/pull/13470#discussion_r1632394832
##########
lucene/core/src/java/org/apache/lucene/search/TopDocs.java:
##########
@@ -350,4 +354,38 @@ private static TopDocs mergeAux(
return new TopFieldDocs(totalHits, hits, sort.getSort());
}
}
+
+ /** Reciprocal Rank Fusion method. */
+ public static TopDocs rrf(int TopN, int k, TopDocs[] hits) {
+ Map<Integer, Float> rrfScore = new HashMap<>();
+ long minHits = Long.MAX_VALUE;
+ for (TopDocs topDoc : hits) {
+ minHits = Math.min(minHits, topDoc.totalHits.value);
+ Map<Integer, Float> scoreMap = new HashMap<>();
+ for (ScoreDoc scoreDoc : topDoc.scoreDocs) {
+ scoreMap.put(scoreDoc.doc, scoreDoc.score);
+ }
+
+ List<Map.Entry<Integer, Float>> scoreList = new
ArrayList<>(scoreMap.entrySet());
+ scoreList.sort(Map.Entry.comparingByValue());
+
+ int rank = 1;
+ for (ScoreDoc scoreDoc : topDoc.scoreDocs) {
+ rrfScore.put(scoreDoc.doc, rrfScore.getOrDefault(scoreDoc.doc, 0.0f) +
1.0f / (rank + k));
Review Comment:
Sounds good! I don't know ```Map#compute``` before tho. It should be like
below:
```
int rank = 1;
for (Map.Entry<Integer, Float> entry : scoreList.entrySet()) {
rrfScore.compute(entry.getKey(), (key, value) ->
(value == null ? 0.0f : value) + 1 / (float)(rank + k)
);
rank++;
}
```
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