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// Copyright Vespa.ai. 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;
class ResultReranker {
private static final Logger logger = Logger.getLogger(ResultReranker.class.getName());
private final HitRescorer hitRescorer;
private final int rerankCount;
private final List<WrappedHit> hitsToRescore = new ArrayList<>();
private final RangeAdjuster ranges = new RangeAdjuster();
ResultReranker(HitRescorer hitRescorer, int rerankCount) {
this.hitRescorer = hitRescorer;
this.rerankCount = rerankCount;
}
void rerankHits(Result result) {
gatherHits(result);
runPreProcessing();
hitRescorer.runNormalizers();
runProcessing();
runPostProcessing();
result.hits().sort();
}
private void gatherHits(Result result) {
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 did not show up here during manual testing.
var wrapped = WrappedHit.from(hit);
if (wrapped != null) hitsToRescore.add(wrapped);
}
}
private void runPreProcessing() {
// we can't be 100% certain that hits were sorted according to relevance:
hitsToRescore.sort(Comparator.naturalOrder());
int count = 0;
for (WrappedHit hit : hitsToRescore) {
if (count == rerankCount) break;
hitRescorer.preprocess(hit);
++count;
}
}
private void runProcessing() {
int count = 0;
for (var iterator = hitsToRescore.iterator(); count < rerankCount && iterator.hasNext(); ) {
WrappedHit wrapped = iterator.next();
double oldScore = wrapped.getScore();
double newScore = hitRescorer.rescoreHit(wrapped);
ranges.withInitialScore(oldScore);
ranges.withFinalScore(newScore);
++count;
iterator.remove();
}
}
private void runPostProcessing() {
// if any hits are left in the list, they may need rescaling:
if (ranges.rescaleNeeded() && ! hitsToRescore.isEmpty()) {
double scale = ranges.scale();
double bias = ranges.bias();
for (WrappedHit wrapped : hitsToRescore) {
double oldScore = wrapped.getScore();
wrapped.setScore(oldScore * scale + bias);
}
}
}
}
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