io.anserini.ltr.feature.SCS Maven / Gradle / Ivy

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/*
 * Anserini: A Lucene toolkit for reproducible information retrieval research
 *
 * Licensed 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 io.anserini.ltr.feature;

import io.anserini.index.Constants;
import io.anserini.ltr.DocumentContext;
import io.anserini.ltr.DocumentFieldContext;
import io.anserini.ltr.FeatureExtractor;
import io.anserini.ltr.QueryContext;
import io.anserini.ltr.QueryFieldContext;

/**
 * SCS = sum (P[t|q]) * log(P[t|q] / P[t|D])
 * page 20 of Carmel, Yom-Tov 2010
 */
public class SCS implements FeatureExtractor {
  private String field;
  private String qfield;

  public SCS() {
    this.field = Constants.CONTENTS;
    this.qfield = "analyzed";
  }

  public SCS(String field, String qfield) {
    this.field = field;
    this.qfield = qfield;
  }

  @Override
  public float extract(DocumentContext documentContext, QueryContext queryContext) {
    DocumentFieldContext context = documentContext.fieldContexts.get(field);
    QueryFieldContext queryFieldContext = queryContext.fieldContexts.get(qfield);
    long termCount = context.totalTermFreq;
    float score = 0.0f;
    for (String token : queryFieldContext.queryFreqs.keySet()) {
      float prtq = queryFieldContext.queryFreqs.get(token) / (float) queryFieldContext.querySize;
      long tf = context.getCollectionFreq(token);
      float prtd = (float)tf/termCount;
      if (prtd == 0) continue;
      score += prtq*Math.log(prtq/prtd);
    }
    return score;
  }

  @Override
  public float postEdit(DocumentContext context, QueryContext queryContext) {
    QueryFieldContext queryFieldContext = queryContext.fieldContexts.get(qfield);
    return queryFieldContext.getSelfLog(context.docId, getName());
  }

  @Override
  public String getName() {
    String name = this.getClass().getSimpleName();
    return String.format("%s_%s_%s",field, qfield,name);
  }

  @Override
  public String getField() {
    return field;
  }

  @Override
  public String getQField() {
    return qfield;
  }

  @Override
  public FeatureExtractor clone() {
    return new SCS(field, qfield);
  }
}