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* 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.search.aggregations.bucket.significant.heuristics;
import org.elasticsearch.ElasticsearchParseException;
import org.elasticsearch.common.io.stream.StreamInput;
import org.elasticsearch.common.io.stream.StreamOutput;
import org.elasticsearch.common.xcontent.XContentBuilder;
import org.elasticsearch.common.xcontent.XContentParser;
import org.elasticsearch.index.query.QueryParseContext;
import org.elasticsearch.index.query.QueryShardException;
import java.io.IOException;
public class JLHScore extends SignificanceHeuristic {
public static final String NAME = "jlh";
public JLHScore() {
}
/**
* Read from a stream.
*/
public JLHScore(StreamInput in) {
// Nothing to read.
}
@Override
public void writeTo(StreamOutput out) throws IOException {
}
@Override
public String getWriteableName() {
return NAME;
}
/**
* Calculates the significance of a term in a sample against a background of
* normal distributions by comparing the changes in frequency. This is the heart
* of the significant terms feature.
*/
@Override
public double getScore(long subsetFreq, long subsetSize, long supersetFreq, long supersetSize) {
checkFrequencyValidity(subsetFreq, subsetSize, supersetFreq, supersetSize, "JLHScore");
if ((subsetSize == 0) || (supersetSize == 0)) {
// avoid any divide by zero issues
return 0;
}
if (supersetFreq == 0) {
// If we are using a background context that is not a strict superset, a foreground
// term may be missing from the background, so for the purposes of this calculation
// we assume a value of 1 for our calculations which avoids returning an "infinity" result
supersetFreq = 1;
}
double subsetProbability = (double) subsetFreq / (double) subsetSize;
double supersetProbability = (double) supersetFreq / (double) supersetSize;
// Using absoluteProbabilityChange alone favours very common words e.g. you, we etc
// because a doubling in popularity of a common term is a big percent difference
// whereas a rare term would have to achieve a hundred-fold increase in popularity to
// achieve the same difference measure.
// In favouring common words as suggested features for search we would get high
// recall but low precision.
double absoluteProbabilityChange = subsetProbability - supersetProbability;
if (absoluteProbabilityChange <= 0) {
return 0;
}
// Using relativeProbabilityChange tends to favour rarer terms e.g.mis-spellings or
// unique URLs.
// A very low-probability term can very easily double in popularity due to the low
// numbers required to do so whereas a high-probability term would have to add many
// extra individual sightings to achieve the same shift.
// In favouring rare words as suggested features for search we would get high
// precision but low recall.
double relativeProbabilityChange = (subsetProbability / supersetProbability);
// A blend of the above metrics - favours medium-rare terms to strike a useful
// balance between precision and recall.
return absoluteProbabilityChange * relativeProbabilityChange;
}
@Override
public XContentBuilder toXContent(XContentBuilder builder, Params params) throws IOException {
builder.startObject(NAME).endObject();
return builder;
}
public static SignificanceHeuristic parse(QueryParseContext context)
throws IOException, QueryShardException {
XContentParser parser = context.parser();
// move to the closing bracket
if (!parser.nextToken().equals(XContentParser.Token.END_OBJECT)) {
throw new ElasticsearchParseException(
"failed to parse [jlh] significance heuristic. expected an empty object, but found [{}] instead",
parser.currentToken());
}
return new JLHScore();
}
@Override
public boolean equals(Object obj) {
if (obj == null || obj.getClass() != getClass()) {
return false;
}
return true;
}
@Override
public int hashCode() {
return getClass().hashCode();
}
public static class JLHScoreBuilder implements SignificanceHeuristicBuilder {
@Override
public XContentBuilder toXContent(XContentBuilder builder, Params params) throws IOException {
builder.startObject(NAME).endObject();
return builder;
}
}
}