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Lucene example source code file (DisjunctionMaxScorer.java)

This example Lucene source code file (DisjunctionMaxScorer.java) is included in the DevDaily.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Java by Example" TM.

Java - Lucene tags/keywords

disjunctionmaxscorer, io, ioexception, ioexception, no_more_docs, no_more_docs, override, override, scorer, scorer, similarity

The Lucene DisjunctionMaxScorer.java source code

package org.apache.lucene.search;

/**
 * Copyright 2004 The Apache Software Foundation
 *
 * 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.
 */

import java.io.IOException;

/**
 * The Scorer for DisjunctionMaxQuery.  The union of all documents generated by the the subquery scorers
 * is generated in document number order.  The score for each document is the maximum of the scores computed
 * by the subquery scorers that generate that document, plus tieBreakerMultiplier times the sum of the scores
 * for the other subqueries that generate the document.
 */
class DisjunctionMaxScorer extends Scorer {

  /* The scorers for subqueries that have remaining docs, kept as a min heap by number of next doc. */
  private final Scorer[] subScorers;
  private int numScorers;
  /* Multiplier applied to non-maximum-scoring subqueries for a document as they are summed into the result. */
  private final float tieBreakerMultiplier;
  private int doc = -1;

  /* Used when scoring currently matching doc. */
  private float scoreSum;
  private float scoreMax;

  /**
   * Creates a new instance of DisjunctionMaxScorer
   * 
   * @param weight
   *          The Weight to be used.
   * @param tieBreakerMultiplier
   *          Multiplier applied to non-maximum-scoring subqueries for a
   *          document as they are summed into the result.
   * @param similarity
   *          -- not used since our definition involves neither coord nor terms
   *          directly
   * @param subScorers
   *          The sub scorers this Scorer should iterate on
   * @param numScorers
   *          The actual number of scorers to iterate on. Note that the array's
   *          length may be larger than the actual number of scorers.
   */
  public DisjunctionMaxScorer(Weight weight, float tieBreakerMultiplier,
      Similarity similarity, Scorer[] subScorers, int numScorers) throws IOException {
    super(similarity, weight);
    this.tieBreakerMultiplier = tieBreakerMultiplier;
    // The passed subScorers array includes only scorers which have documents
    // (DisjunctionMaxQuery takes care of that), and their nextDoc() was already
    // called.
    this.subScorers = subScorers;
    this.numScorers = numScorers;
    
    heapify();
  }

  @Override
  public int nextDoc() throws IOException {
    if (numScorers == 0) return doc = NO_MORE_DOCS;
    while (subScorers[0].docID() == doc) {
      if (subScorers[0].nextDoc() != NO_MORE_DOCS) {
        heapAdjust(0);
      } else {
        heapRemoveRoot();
        if (numScorers == 0) {
          return doc = NO_MORE_DOCS;
        }
      }
    }
    
    return doc = subScorers[0].docID();
  }

  @Override
  public int docID() {
    return doc;
  }

  /** Determine the current document score.  Initially invalid, until {@link #nextDoc()} is called the first time.
   * @return the score of the current generated document
   */
  @Override
  public float score() throws IOException {
    int doc = subScorers[0].docID();
    scoreSum = scoreMax = subScorers[0].score();
    int size = numScorers;
    scoreAll(1, size, doc);
    scoreAll(2, size, doc);
    return scoreMax + (scoreSum - scoreMax) * tieBreakerMultiplier;
  }

  // Recursively iterate all subScorers that generated last doc computing sum and max
  private void scoreAll(int root, int size, int doc) throws IOException {
    if (root < size && subScorers[root].docID() == doc) {
      float sub = subScorers[root].score();
      scoreSum += sub;
      scoreMax = Math.max(scoreMax, sub);
      scoreAll((root<<1)+1, size, doc);
      scoreAll((root<<1)+2, size, doc);
    }
  }

  @Override
  public int advance(int target) throws IOException {
    if (numScorers == 0) return doc = NO_MORE_DOCS;
    while (subScorers[0].docID() < target) {
      if (subScorers[0].advance(target) != NO_MORE_DOCS) {
        heapAdjust(0);
      } else {
        heapRemoveRoot();
        if (numScorers == 0) {
          return doc = NO_MORE_DOCS;
        }
      }
    }
    return doc = subScorers[0].docID();
  }

  // Organize subScorers into a min heap with scorers generating the earliest document on top.
  private void heapify() {
    for (int i = (numScorers >> 1) - 1; i >= 0; i--) {
      heapAdjust(i);
    }
  }

  /* The subtree of subScorers at root is a min heap except possibly for its root element.
   * Bubble the root down as required to make the subtree a heap.
   */
  private void heapAdjust(int root) {
    Scorer scorer = subScorers[root];
    int doc = scorer.docID();
    int i = root;
    while (i <= (numScorers >> 1) - 1) {
      int lchild = (i << 1) + 1;
      Scorer lscorer = subScorers[lchild];
      int ldoc = lscorer.docID();
      int rdoc = Integer.MAX_VALUE, rchild = (i << 1) + 2;
      Scorer rscorer = null;
      if (rchild < numScorers) {
        rscorer = subScorers[rchild];
        rdoc = rscorer.docID();
      }
      if (ldoc < doc) {
        if (rdoc < ldoc) {
          subScorers[i] = rscorer;
          subScorers[rchild] = scorer;
          i = rchild;
        } else {
          subScorers[i] = lscorer;
          subScorers[lchild] = scorer;
          i = lchild;
        }
      } else if (rdoc < doc) {
        subScorers[i] = rscorer;
        subScorers[rchild] = scorer;
        i = rchild;
      } else {
        return;
      }
    }
  }

  // Remove the root Scorer from subScorers and re-establish it as a heap
  private void heapRemoveRoot() {
    if (numScorers == 1) {
      subScorers[0] = null;
      numScorers = 0;
    } else {
      subScorers[0] = subScorers[numScorers - 1];
      subScorers[numScorers - 1] = null;
      --numScorers;
      heapAdjust(0);
    }
  }

}

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