DistanceComparatorSource.java

package lia.extsearch.sorting;

/**
 * Copyright Manning Publications Co.
 *
 * 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 lan      
*/

import org.apache.lucene.search.SortField;
import org.apache.lucene.search.FieldComparatorSource;
import org.apache.lucene.search.FieldComparator;
import org.apache.lucene.search.FieldCache;
import org.apache.lucene.index.IndexReader;
import org.apache.lucene.index.TermEnum;
import org.apache.lucene.index.Term;

import java.io.IOException;

// From chapter 6
public class DistanceComparatorSource
  extends FieldComparatorSource {                 // #1
  private int x;
  private int y;

  public DistanceComparatorSource(int x, int y) { // #2
    this.x = x;
    this.y = y;
  }

  public FieldComparator newComparator(java.lang.String fieldName,   // #3
                                       int numHits, int sortPos,   // #3
                                       boolean reversed)   // #3
    throws IOException {       // #3
    return new DistanceScoreDocLookupComparator(fieldName,
                                                numHits);
  }

  private class DistanceScoreDocLookupComparator  // #4
      extends FieldComparator {
    private int[] xDoc, yDoc;                     // #5
    private float[] values;                       // #6
    private float bottom;                         // #7
    String fieldName;

    public DistanceScoreDocLookupComparator(
                  String fieldName, int numHits) throws IOException {
      values = new float[numHits];
      this.fieldName = fieldName;
    }

    public void setNextReader(IndexReader reader, int docBase) throws IOException {
      xDoc = FieldCache.DEFAULT.getInts(reader, "x");  // #8
      yDoc = FieldCache.DEFAULT.getInts(reader, "y");  // #8
    }

    private float getDistance(int doc) {              // #9
      int deltax = xDoc[doc] - x;                     // #9
      int deltay = yDoc[doc] - y;                     // #9
      return (float) Math.sqrt(deltax * deltax + deltay * deltay); // #9
    }

    public int compare(int slot1, int slot2) {          // #10
      if (values[slot1] < values[slot2]) return -1;     // #10
      if (values[slot1] > values[slot2]) return 1;      // #10
      return 0;                                         // #10
    }

    public void setBottom(int slot) {                   // #11
      bottom = values[slot];
    }

    public int compareBottom(int doc) {                 // #12
      float docDistance = getDistance(doc);
      if (bottom < docDistance) return -1;              // #12
      if (bottom > docDistance) return 1;               // #12
      return 0;                                         // #12
    }

    public void copy(int slot, int doc) {               // #13
      values[slot] = getDistance(doc);                  // #13
    }

    public Comparable value(int slot) {                 // #14
      return new Float(values[slot]);                   // #14
    }                                                   // #14

    public int sortType() {
      return SortField.CUSTOM;
    }
  }

  public String toString() {
    return "Distance from ("+x+","+y+")";
  }
}

/*
#1 Extend FieldComparatorSource
#2 Give constructor base location
#3 Create comparator
#4 FieldComparator implementation
#5 Array of x, y per document
#6 Distances for documents in the queue
#7 Worst distance in the queue
#8 Get x, y values from field cache
#9 Compute distance for one document
#10 Compare two docs in the top N
#11 Record worst scoring doc in the top N
#12 Compare new doc to worst scoring doc
#13 Insert new doc into top N
#14 Extract value from top N
*/