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/*
* 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.search.suggest.phrase;
import org.apache.lucene.index.IndexReader;
import org.apache.lucene.index.Terms;
import org.apache.lucene.util.BytesRef;
import org.elasticsearch.common.ParseField;
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.common.xcontent.XContentParser.Token;
import org.elasticsearch.index.query.QueryParseContext;
import org.elasticsearch.search.suggest.phrase.WordScorer.WordScorerFactory;
import java.io.IOException;
import java.util.Objects;
/**
* An <a href="http://en.wikipedia.org/wiki/Additive_smoothing">additive
* smoothing</a> model.
* <p>
* See <a
* href="http://en.wikipedia.org/wiki/N-gram#Smoothing_techniques">N-Gram
* Smoothing</a> for details.
* </p>
*/
public final class Laplace extends SmoothingModel {
public static final String NAME = "laplace";
private static final ParseField ALPHA_FIELD = new ParseField("alpha");
static final ParseField PARSE_FIELD = new ParseField(NAME);
/**
* Default alpha parameter for laplace smoothing
*/
public static final double DEFAULT_LAPLACE_ALPHA = 0.5;
private double alpha = DEFAULT_LAPLACE_ALPHA;
/**
* Creates a Laplace smoothing model.
*
*/
public Laplace(double alpha) {
this.alpha = alpha;
}
/**
* Read from a stream.
*/
public Laplace(StreamInput in) throws IOException {
alpha = in.readDouble();
}
@Override
public void writeTo(StreamOutput out) throws IOException {
out.writeDouble(alpha);
}
/**
* @return the laplace model alpha parameter
*/
public double getAlpha() {
return this.alpha;
}
@Override
protected XContentBuilder innerToXContent(XContentBuilder builder, Params params) throws IOException {
builder.field(ALPHA_FIELD.getPreferredName(), alpha);
return builder;
}
@Override
public String getWriteableName() {
return NAME;
}
@Override
protected boolean doEquals(SmoothingModel other) {
Laplace otherModel = (Laplace) other;
return Objects.equals(alpha, otherModel.alpha);
}
@Override
protected final int doHashCode() {
return Objects.hash(alpha);
}
public static SmoothingModel innerFromXContent(QueryParseContext parseContext) throws IOException {
XContentParser parser = parseContext.parser();
XContentParser.Token token;
String fieldName = null;
double alpha = DEFAULT_LAPLACE_ALPHA;
while ((token = parser.nextToken()) != Token.END_OBJECT) {
if (token == XContentParser.Token.FIELD_NAME) {
fieldName = parser.currentName();
}
if (token.isValue() && parseContext.parseFieldMatcher().match(fieldName, ALPHA_FIELD)) {
alpha = parser.doubleValue();
}
}
return new Laplace(alpha);
}
@Override
public WordScorerFactory buildWordScorerFactory() {
return (IndexReader reader, Terms terms, String field, double realWordLikelyhood, BytesRef separator)
-> new LaplaceScorer(reader, terms, field, realWordLikelyhood, separator, alpha);
}
}
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