Add Expected Reciprocal Rank metric (#31891)

This change adds Expected Reciprocal Rank (ERR) as a ranking evaluation metric
as descriped in:

Chapelle, O., Metlzer, D., Zhang, Y., & Grinspan, P. (2009).
Expected reciprocal rank for graded relevance.
Proceeding of the 18th ACM Conference on Information and Knowledge Management.
https://doi.org/10.1145/1645953.1646033

ERR is an extension of the classical reciprocal rank to the graded relevance
case and assumes a cascade browsing model. It quantifies the usefulness of a
document at rank `i` conditioned on the degree of relevance of the items at ranks
less than `i`. ERR seems to be gain traction as an alternative to (n)DCG, so it
seems like a good metric to support. Also ERR seems to be the default optimization
metric used for training in RankLib, a widely used learning to rank library.

Relates to #29653
This commit is contained in:
Christoph Büscher 2018-07-12 15:50:58 +02:00 committed by GitHub
parent 6fcd606536
commit 4ae4ac08d5
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5 changed files with 522 additions and 9 deletions

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@ -294,6 +294,7 @@ public final class ConstructingObjectParser<Value, Context> extends AbstractObje
}
}
@Override
public String getName() {
return objectParser.getName();
}

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@ -326,9 +326,9 @@ public class DiscountedCumulativeGain implements EvaluationMetric {
return false;
}
DiscountedCumulativeGain.Detail other = (DiscountedCumulativeGain.Detail) obj;
return (this.dcg == other.dcg &&
this.idcg == other.idcg &&
this.unratedDocs == other.unratedDocs);
return Double.compare(this.dcg, other.dcg) == 0 &&
Double.compare(this.idcg, other.idcg) == 0 &&
this.unratedDocs == other.unratedDocs;
}
@Override

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@ -0,0 +1,295 @@
/*
* Licensed to Elasticsearch under one or more contributor
* license agreements. See the NOTICE file distributed with
* this work for additional information regarding copyright
* ownership. Elasticsearch 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.elasticsearch.index.rankeval;
import org.elasticsearch.common.Nullable;
import org.elasticsearch.common.ParseField;
import org.elasticsearch.common.io.stream.StreamInput;
import org.elasticsearch.common.io.stream.StreamOutput;
import org.elasticsearch.common.xcontent.ConstructingObjectParser;
import org.elasticsearch.common.xcontent.XContentBuilder;
import org.elasticsearch.common.xcontent.XContentParser;
import org.elasticsearch.search.SearchHit;
import java.io.IOException;
import java.util.ArrayList;
import java.util.List;
import java.util.Objects;
import java.util.Optional;
import static org.elasticsearch.common.xcontent.ConstructingObjectParser.constructorArg;
import static org.elasticsearch.common.xcontent.ConstructingObjectParser.optionalConstructorArg;
import static org.elasticsearch.index.rankeval.EvaluationMetric.joinHitsWithRatings;
/**
* Implementation of the Expected Reciprocal Rank metric described in:<p>
*
* Chapelle, O., Metlzer, D., Zhang, Y., &amp; Grinspan, P. (2009).<br>
* Expected reciprocal rank for graded relevance.<br>
* Proceeding of the 18th ACM Conference on Information and Knowledge Management - CIKM 09, 621.<br>
* https://doi.org/10.1145/1645953.1646033
*/
public class ExpectedReciprocalRank implements EvaluationMetric {
/** the default search window size */
private static final int DEFAULT_K = 10;
/** the search window size */
private final int k;
/**
* Optional. If set, this will be the rating for docs that are unrated in the ranking evaluation request
*/
private final Integer unknownDocRating;
private final int maxRelevance;
private final double two_pow_maxRelevance;
public static final String NAME = "expected_reciprocal_rank";
public ExpectedReciprocalRank(int maxRelevance) {
this(maxRelevance, null, DEFAULT_K);
}
/**
* @param maxRelevance
* the maximal relevance judgment in the evaluation dataset
* @param unknownDocRating
* the rating for documents the user hasn't supplied an explicit
* rating for. Can be {@code null}, in which case document is
* skipped.
* @param k
* the search window size all request use.
*/
public ExpectedReciprocalRank(int maxRelevance, @Nullable Integer unknownDocRating, int k) {
this.maxRelevance = maxRelevance;
this.unknownDocRating = unknownDocRating;
this.k = k;
// we can pre-calculate the constant used in metric calculation
this.two_pow_maxRelevance = Math.pow(2, this.maxRelevance);
}
ExpectedReciprocalRank(StreamInput in) throws IOException {
this.maxRelevance = in.readVInt();
this.unknownDocRating = in.readOptionalVInt();
this.k = in.readVInt();
this.two_pow_maxRelevance = Math.pow(2, this.maxRelevance);
}
@Override
public void writeTo(StreamOutput out) throws IOException {
out.writeVInt(maxRelevance);
out.writeOptionalVInt(unknownDocRating);
out.writeVInt(k);
}
@Override
public String getWriteableName() {
return NAME;
}
int getK() {
return this.k;
}
int getMaxRelevance() {
return this.maxRelevance;
}
/**
* get the rating used for unrated documents
*/
public Integer getUnknownDocRating() {
return this.unknownDocRating;
}
@Override
public Optional<Integer> forcedSearchSize() {
return Optional.of(k);
}
@Override
public EvalQueryQuality evaluate(String taskId, SearchHit[] hits, List<RatedDocument> ratedDocs) {
List<RatedSearchHit> ratedHits = joinHitsWithRatings(hits, ratedDocs);
if (ratedHits.size() > this.k) {
ratedHits = ratedHits.subList(0, k);
}
List<Integer> ratingsInSearchHits = new ArrayList<>(ratedHits.size());
int unratedResults = 0;
for (RatedSearchHit hit : ratedHits) {
// unknownDocRating might be null, in which case unrated will be ignored in the calculation.
// we still need to add them as a placeholder so the rank of the subsequent ratings is correct
ratingsInSearchHits.add(hit.getRating().orElse(unknownDocRating));
if (hit.getRating().isPresent() == false) {
unratedResults++;
}
}
double p = 1;
double err = 0;
int rank = 1;
for (Integer rating : ratingsInSearchHits) {
if (rating != null) {
double probR = probabilityOfRelevance(rating);
err = err + (p * probR / rank);
p = p * (1 - probR);
}
rank++;
}
EvalQueryQuality evalQueryQuality = new EvalQueryQuality(taskId, err);
evalQueryQuality.addHitsAndRatings(ratedHits);
evalQueryQuality.setMetricDetails(new Detail(unratedResults));
return evalQueryQuality;
}
double probabilityOfRelevance(Integer rating) {
return (Math.pow(2, rating) - 1) / this.two_pow_maxRelevance;
}
private static final ParseField K_FIELD = new ParseField("k");
private static final ParseField UNKNOWN_DOC_RATING_FIELD = new ParseField("unknown_doc_rating");
private static final ParseField MAX_RELEVANCE_FIELD = new ParseField("maximum_relevance");
private static final ConstructingObjectParser<ExpectedReciprocalRank, Void> PARSER = new ConstructingObjectParser<>("dcg", false,
args -> {
int maxRelevance = (Integer) args[0];
Integer optK = (Integer) args[2];
return new ExpectedReciprocalRank(maxRelevance, (Integer) args[1],
optK == null ? DEFAULT_K : optK);
});
static {
PARSER.declareInt(constructorArg(), MAX_RELEVANCE_FIELD);
PARSER.declareInt(optionalConstructorArg(), UNKNOWN_DOC_RATING_FIELD);
PARSER.declareInt(optionalConstructorArg(), K_FIELD);
}
public static ExpectedReciprocalRank fromXContent(XContentParser parser) {
return PARSER.apply(parser, null);
}
@Override
public XContentBuilder toXContent(XContentBuilder builder, Params params) throws IOException {
builder.startObject();
builder.startObject(NAME);
builder.field(MAX_RELEVANCE_FIELD.getPreferredName(), this.maxRelevance);
if (unknownDocRating != null) {
builder.field(UNKNOWN_DOC_RATING_FIELD.getPreferredName(), this.unknownDocRating);
}
builder.field(K_FIELD.getPreferredName(), this.k);
builder.endObject();
builder.endObject();
return builder;
}
@Override
public final boolean equals(Object obj) {
if (this == obj) {
return true;
}
if (obj == null || getClass() != obj.getClass()) {
return false;
}
ExpectedReciprocalRank other = (ExpectedReciprocalRank) obj;
return this.k == other.k &&
this.maxRelevance == other.maxRelevance
&& Objects.equals(unknownDocRating, other.unknownDocRating);
}
@Override
public final int hashCode() {
return Objects.hash(unknownDocRating, k, maxRelevance);
}
public static final class Detail implements MetricDetail {
private static ParseField UNRATED_FIELD = new ParseField("unrated_docs");
private final int unratedDocs;
Detail(int unratedDocs) {
this.unratedDocs = unratedDocs;
}
Detail(StreamInput in) throws IOException {
this.unratedDocs = in.readVInt();
}
@Override
public
String getMetricName() {
return NAME;
}
@Override
public XContentBuilder innerToXContent(XContentBuilder builder, Params params) throws IOException {
return builder.field(UNRATED_FIELD.getPreferredName(), this.unratedDocs);
}
private static final ConstructingObjectParser<Detail, Void> PARSER = new ConstructingObjectParser<>(NAME, true, args -> {
return new Detail((Integer) args[0]);
});
static {
PARSER.declareInt(constructorArg(), UNRATED_FIELD);
}
public static Detail fromXContent(XContentParser parser) {
return PARSER.apply(parser, null);
}
@Override
public void writeTo(StreamOutput out) throws IOException {
out.writeVInt(this.unratedDocs);
}
@Override
public String getWriteableName() {
return NAME;
}
/**
* @return the number of unrated documents in the search results
*/
public Object getUnratedDocs() {
return this.unratedDocs;
}
@Override
public boolean equals(Object obj) {
if (this == obj) {
return true;
}
if (obj == null || getClass() != obj.getClass()) {
return false;
}
ExpectedReciprocalRank.Detail other = (ExpectedReciprocalRank.Detail) obj;
return this.unratedDocs == other.unratedDocs;
}
@Override
public int hashCode() {
return Objects.hash(this.unratedDocs);
}
}
}

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@ -55,7 +55,7 @@ public class DiscountedCumulativeGainTests extends ESTestCase {
/**
* Assuming the docs are ranked in the following order:
*
* rank | rel_rank | 2^(rel_rank) - 1 | log_2(rank + 1) | (2^(rel_rank) - 1) / log_2(rank + 1)
* rank | relevance | 2^(relevance) - 1 | log_2(rank + 1) | (2^(relevance) - 1) / log_2(rank + 1)
* -------------------------------------------------------------------------------------------
* 1 | 3 | 7.0 | 1.0 | 7.0 | 7.0 | 
* 2 | 2 | 3.0 | 1.5849625007211563 | 1.8927892607143721
@ -82,7 +82,7 @@ public class DiscountedCumulativeGainTests extends ESTestCase {
* Check with normalization: to get the maximal possible dcg, sort documents by
* relevance in descending order
*
* rank | rel_rank | 2^(rel_rank) - 1 | log_2(rank + 1) | (2^(rel_rank) - 1) / log_2(rank + 1)
* rank | relevance | 2^(relevance) - 1 | log_2(rank + 1) | (2^(relevance) - 1) / log_2(rank + 1)
* ---------------------------------------------------------------------------------------
* 1 | 3 | 7.0 | 1.0  | 7.0
* 2 | 3 | 7.0 | 1.5849625007211563 | 4.416508275000202
@ -101,7 +101,7 @@ public class DiscountedCumulativeGainTests extends ESTestCase {
* This tests metric when some documents in the search result don't have a
* rating provided by the user.
*
* rank | rel_rank | 2^(rel_rank) - 1 | log_2(rank + 1) | (2^(rel_rank) - 1) / log_2(rank + 1)
* rank | relevance | 2^(relevance) - 1 | log_2(rank + 1) | (2^(relevance) - 1) / log_2(rank + 1)
* -------------------------------------------------------------------------------------------
* 1 | 3 | 7.0 | 1.0 | 7.0 2 | 
* 2 | 3.0 | 1.5849625007211563 | 1.8927892607143721
@ -134,7 +134,7 @@ public class DiscountedCumulativeGainTests extends ESTestCase {
* Check with normalization: to get the maximal possible dcg, sort documents by
* relevance in descending order
*
* rank | rel_rank | 2^(rel_rank) - 1 | log_2(rank + 1) | (2^(rel_rank) - 1) / log_2(rank + 1)
* rank | relevance | 2^(relevance) - 1 | log_2(rank + 1) | (2^(relevance) - 1) / log_2(rank + 1)
* ----------------------------------------------------------------------------------------
* 1 | 3 | 7.0 | 1.0  | 7.0
* 2 | 3 | 7.0 | 1.5849625007211563 | 4.416508275000202
@ -154,7 +154,7 @@ public class DiscountedCumulativeGainTests extends ESTestCase {
* documents than search hits because we restrict DCG to be calculated at the
* fourth position
*
* rank | rel_rank | 2^(rel_rank) - 1 | log_2(rank + 1) | (2^(rel_rank) - 1) / log_2(rank + 1)
* rank | relevance | 2^(relevance) - 1 | log_2(rank + 1) | (2^(relevance) - 1) / log_2(rank + 1)
* -------------------------------------------------------------------------------------------
* 1 | 3 | 7.0 | 1.0 | 7.0 2 | 
* 2 | 3.0 | 1.5849625007211563 | 1.8927892607143721
@ -191,7 +191,7 @@ public class DiscountedCumulativeGainTests extends ESTestCase {
* Check with normalization: to get the maximal possible dcg, sort documents by
* relevance in descending order
*
* rank | rel_rank | 2^(rel_rank) - 1 | log_2(rank + 1) | (2^(rel_rank) - 1) / log_2(rank + 1)
* rank | relevance | 2^(relevance) - 1 | log_2(rank + 1) | (2^(relevance) - 1) / log_2(rank + 1)
* ---------------------------------------------------------------------------------------
* 1 | 3 | 7.0 | 1.0  | 7.0
* 2 | 3 | 7.0 | 1.5849625007211563 | 4.416508275000202

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@ -0,0 +1,217 @@
/*
* Licensed to Elasticsearch under one or more contributor
* license agreements. See the NOTICE file distributed with
* this work for additional information regarding copyright
* ownership. Elasticsearch 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.elasticsearch.index.rankeval;
import org.elasticsearch.common.bytes.BytesReference;
import org.elasticsearch.common.io.stream.NamedWriteableRegistry;
import org.elasticsearch.common.text.Text;
import org.elasticsearch.common.xcontent.ToXContent;
import org.elasticsearch.common.xcontent.XContentBuilder;
import org.elasticsearch.common.xcontent.XContentFactory;
import org.elasticsearch.common.xcontent.XContentParseException;
import org.elasticsearch.common.xcontent.XContentParser;
import org.elasticsearch.common.xcontent.XContentType;
import org.elasticsearch.common.xcontent.json.JsonXContent;
import org.elasticsearch.index.Index;
import org.elasticsearch.search.SearchHit;
import org.elasticsearch.search.SearchShardTarget;
import org.elasticsearch.test.ESTestCase;
import java.io.IOException;
import java.util.ArrayList;
import java.util.Collections;
import java.util.List;
import static org.elasticsearch.test.EqualsHashCodeTestUtils.checkEqualsAndHashCode;
import static org.elasticsearch.test.XContentTestUtils.insertRandomFields;
import static org.hamcrest.CoreMatchers.containsString;
public class ExpectedReciprocalRankTests extends ESTestCase {
private static final double DELTA = 10E-14;
public void testProbabilityOfRelevance() {
ExpectedReciprocalRank err = new ExpectedReciprocalRank(5);
assertEquals(0.0, err.probabilityOfRelevance(0), 0.0);
assertEquals(1d/32d, err.probabilityOfRelevance(1), 0.0);
assertEquals(3d/32d, err.probabilityOfRelevance(2), 0.0);
assertEquals(7d/32d, err.probabilityOfRelevance(3), 0.0);
assertEquals(15d/32d, err.probabilityOfRelevance(4), 0.0);
assertEquals(31d/32d, err.probabilityOfRelevance(5), 0.0);
}
/**
* Assuming the result ranking is
*
* <pre>{@code
* rank | relevance | probR / r | p | p * probR / r
* -------------------------------------------------------
* 1 | 3 | 0.875 | 1 | 0.875 |
* 2 | 2 | 0.1875 | 0.125 | 0.0234375 |
* 3 | 0 | 0 | 0.078125 | 0 |
* 4 | 1 | 0.03125 | 0.078125 | 0.00244140625 |
* }</pre>
*
* err => sum of last column
*/
public void testERRAt() {
List<RatedDocument> rated = new ArrayList<>();
Integer[] relevanceRatings = new Integer[] { 3, 2, 0, 1};
SearchHit[] hits = createSearchHits(rated, relevanceRatings);
ExpectedReciprocalRank err = new ExpectedReciprocalRank(3, 0, 3);
assertEquals(0.8984375, err.evaluate("id", hits, rated).getQualityLevel(), DELTA);
// take 4th rank into window
err = new ExpectedReciprocalRank(3, 0, 4);
assertEquals(0.8984375 + 0.00244140625, err.evaluate("id", hits, rated).getQualityLevel(), DELTA);
}
/**
* Assuming the result ranking is
*
* <pre>{@code
* rank | relevance | probR / r | p | p * probR / r
* -------------------------------------------------------
* 1 | 3 | 0.875 | 1 | 0.875 |
* 2 | n/a | n/a | 0.125 | n/a |
* 3 | 0 | 0 | 0.125 | 0 |
* 4 | 1 | 0.03125 | 0.125 | 0.00390625 |
* }</pre>
*
* err => sum of last column
*/
public void testERRMissingRatings() {
List<RatedDocument> rated = new ArrayList<>();
Integer[] relevanceRatings = new Integer[] { 3, null, 0, 1};
SearchHit[] hits = createSearchHits(rated, relevanceRatings);
ExpectedReciprocalRank err = new ExpectedReciprocalRank(3, null, 4);
EvalQueryQuality evaluation = err.evaluate("id", hits, rated);
assertEquals(0.875 + 0.00390625, evaluation.getQualityLevel(), DELTA);
assertEquals(1, ((ExpectedReciprocalRank.Detail) evaluation.getMetricDetails()).getUnratedDocs());
// if we supply e.g. 2 as unknown docs rating, it should be the same as in the other test above
err = new ExpectedReciprocalRank(3, 2, 4);
assertEquals(0.8984375 + 0.00244140625, err.evaluate("id", hits, rated).getQualityLevel(), DELTA);
}
private SearchHit[] createSearchHits(List<RatedDocument> rated, Integer[] relevanceRatings) {
SearchHit[] hits = new SearchHit[relevanceRatings.length];
for (int i = 0; i < relevanceRatings.length; i++) {
if (relevanceRatings[i] != null) {
rated.add(new RatedDocument("index", Integer.toString(i), relevanceRatings[i]));
}
hits[i] = new SearchHit(i, Integer.toString(i), new Text("type"), Collections.emptyMap());
hits[i].shard(new SearchShardTarget("testnode", new Index("index", "uuid"), 0, null));
}
return hits;
}
/**
* test that metric returns 0.0 when there are no search results
*/
public void testNoResults() throws Exception {
ExpectedReciprocalRank err = new ExpectedReciprocalRank(5, 0, 10);
assertEquals(0.0, err.evaluate("id", new SearchHit[0], Collections.emptyList()).getQualityLevel(), DELTA);
}
public void testParseFromXContent() throws IOException {
assertParsedCorrect("{ \"unknown_doc_rating\": 2, \"maximum_relevance\": 5, \"k\" : 15 }", 2, 5, 15);
assertParsedCorrect("{ \"unknown_doc_rating\": 2, \"maximum_relevance\": 4 }", 2, 4, 10);
assertParsedCorrect("{ \"maximum_relevance\": 4, \"k\": 23 }", null, 4, 23);
}
private void assertParsedCorrect(String xContent, Integer expectedUnknownDocRating, int expectedMaxRelevance, int expectedK)
throws IOException {
try (XContentParser parser = createParser(JsonXContent.jsonXContent, xContent)) {
ExpectedReciprocalRank errAt = ExpectedReciprocalRank.fromXContent(parser);
assertEquals(expectedUnknownDocRating, errAt.getUnknownDocRating());
assertEquals(expectedK, errAt.getK());
assertEquals(expectedMaxRelevance, errAt.getMaxRelevance());
}
}
public static ExpectedReciprocalRank createTestItem() {
Integer unknownDocRating = frequently() ? Integer.valueOf(randomIntBetween(0, 10)) : null;
int maxRelevance = randomIntBetween(1, 10);
return new ExpectedReciprocalRank(maxRelevance, unknownDocRating, randomIntBetween(1, 10));
}
public void testXContentRoundtrip() throws IOException {
ExpectedReciprocalRank testItem = createTestItem();
XContentBuilder builder = XContentFactory.contentBuilder(randomFrom(XContentType.values()));
XContentBuilder shuffled = shuffleXContent(testItem.toXContent(builder, ToXContent.EMPTY_PARAMS));
try (XContentParser itemParser = createParser(shuffled)) {
itemParser.nextToken();
itemParser.nextToken();
ExpectedReciprocalRank parsedItem = ExpectedReciprocalRank.fromXContent(itemParser);
assertNotSame(testItem, parsedItem);
assertEquals(testItem, parsedItem);
assertEquals(testItem.hashCode(), parsedItem.hashCode());
}
}
public void testXContentParsingIsNotLenient() throws IOException {
ExpectedReciprocalRank testItem = createTestItem();
XContentType xContentType = randomFrom(XContentType.values());
BytesReference originalBytes = toShuffledXContent(testItem, xContentType, ToXContent.EMPTY_PARAMS, randomBoolean());
BytesReference withRandomFields = insertRandomFields(xContentType, originalBytes, null, random());
try (XContentParser parser = createParser(xContentType.xContent(), withRandomFields)) {
parser.nextToken();
parser.nextToken();
XContentParseException exception = expectThrows(XContentParseException.class,
() -> DiscountedCumulativeGain.fromXContent(parser));
assertThat(exception.getMessage(), containsString("[dcg] unknown field"));
}
}
public void testMetricDetails() {
int unratedDocs = randomIntBetween(0, 100);
ExpectedReciprocalRank.Detail detail = new ExpectedReciprocalRank.Detail(unratedDocs);
assertEquals(unratedDocs, detail.getUnratedDocs());
}
public void testSerialization() throws IOException {
ExpectedReciprocalRank original = createTestItem();
ExpectedReciprocalRank deserialized = ESTestCase.copyWriteable(original, new NamedWriteableRegistry(Collections.emptyList()),
ExpectedReciprocalRank::new);
assertEquals(deserialized, original);
assertEquals(deserialized.hashCode(), original.hashCode());
assertNotSame(deserialized, original);
}
public void testEqualsAndHash() throws IOException {
checkEqualsAndHashCode(createTestItem(), original -> {
return new ExpectedReciprocalRank(original.getMaxRelevance(), original.getUnknownDocRating(), original.getK());
}, ExpectedReciprocalRankTests::mutateTestItem);
}
private static ExpectedReciprocalRank mutateTestItem(ExpectedReciprocalRank original) {
switch (randomIntBetween(0, 2)) {
case 0:
return new ExpectedReciprocalRank(original.getMaxRelevance() + 1, original.getUnknownDocRating(), original.getK());
case 1:
return new ExpectedReciprocalRank(original.getMaxRelevance(),
randomValueOtherThan(original.getUnknownDocRating(), () -> randomIntBetween(0, 10)), original.getK());
case 2:
return new ExpectedReciprocalRank(original.getMaxRelevance(), original.getUnknownDocRating(),
randomValueOtherThan(original.getK(), () -> randomIntBetween(1, 10)));
default:
throw new IllegalArgumentException("mutation variant not allowed");
}
}
}