diff options
Diffstat (limited to 'container-search/src/main/java/com/yahoo/search/ranking/ResultReranker.java')
-rw-r--r-- | container-search/src/main/java/com/yahoo/search/ranking/ResultReranker.java | 91 |
1 files changed, 91 insertions, 0 deletions
diff --git a/container-search/src/main/java/com/yahoo/search/ranking/ResultReranker.java b/container-search/src/main/java/com/yahoo/search/ranking/ResultReranker.java new file mode 100644 index 00000000000..e700276b151 --- /dev/null +++ b/container-search/src/main/java/com/yahoo/search/ranking/ResultReranker.java @@ -0,0 +1,91 @@ +// Copyright Yahoo. Licensed under the terms of the Apache 2.0 license. See LICENSE in the project root. +package com.yahoo.search.ranking; + +import com.yahoo.search.Result; +import com.yahoo.search.result.Hit; +import com.yahoo.search.result.HitGroup; + +import java.util.ArrayList; +import java.util.Comparator; +import java.util.List; +import java.util.logging.Logger; + +public class ResultReranker { + + private static final Logger logger = Logger.getLogger(ResultReranker.class.getName()); + + // scale and adjust the score according to the range + // of the original and final score values to avoid that + // a score from the backend is larger than finalScores_low + static class Ranges { + private double initialScores_high = -Double.MAX_VALUE; + private double initialScores_low = Double.MAX_VALUE; + private double finalScores_high = -Double.MAX_VALUE; + private double finalScores_low = Double.MAX_VALUE; + + boolean valid() { + return (initialScores_high >= initialScores_low + && + finalScores_high >= finalScores_low); + } + void withInitialScore(double score) { + if (score < initialScores_low) initialScores_low = score; + if (score > initialScores_high) initialScores_high = score; + } + void withFinalScore(double score) { + if (score < finalScores_low) finalScores_low = score; + if (score > finalScores_high) finalScores_high = score; + } + private double initialRange() { + double r = initialScores_high - initialScores_low; + if (r < 1.0) r = 1.0; + return r; + } + private double finalRange() { + double r = finalScores_high - finalScores_low; + if (r < 1.0) r = 1.0; + return r; + } + double scale() { return finalRange() / initialRange(); } + double bias() { return finalScores_low - initialScores_low * scale(); } + } + + static void rerankHits(Result result, HitRescorer hitRescorer, int rerankCount) { + List<Hit> hitsToRescore = new ArrayList<>(); + // consider doing recursive iteration explicitly instead of using deepIterator? + for (var iterator = result.hits().deepIterator(); iterator.hasNext();) { + Hit hit = iterator.next(); + if (hit.isMeta() || hit instanceof HitGroup) { + continue; + } + // what about hits inside grouping results? + // they are inside GroupingListHit, we won't recurse into it; so we won't see them. + hitsToRescore.add(hit); + } + // we can't be 100% certain that hits were sorted according to relevance: + hitsToRescore.sort(Comparator.naturalOrder()); + var ranges = new Ranges(); + for (var iterator = hitsToRescore.iterator(); rerankCount > 0 && iterator.hasNext(); ) { + Hit hit = iterator.next(); + double oldScore = hit.getRelevance().getScore(); + boolean didRerank = hitRescorer.rescoreHit(hit); + if (didRerank) { + ranges.withInitialScore(oldScore); + ranges.withFinalScore(hit.getRelevance().getScore()); + --rerankCount; + iterator.remove(); + } + } + // if any hits are left in the list, they need rescaling: + if (ranges.valid()) { + double scale = ranges.scale(); + double bias = ranges.bias(); + for (Hit hit : hitsToRescore) { + double oldScore = hit.getRelevance().getScore(); + hit.setRelevance(oldScore * scale + bias); + } + } + result.hits().sort(); + } + +} |