DisjunctionMaxScorer.cs
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上传日期:2013-09-30
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- /*
- * Copyright 2005 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.
- */
- using System;
- namespace Lucene.Net.Search
- {
-
- /// <summary> The Scorer for DisjunctionMaxQuery's. 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.
- /// </summary>
- /// <author> Chuck Williams
- /// </author>
- class DisjunctionMaxScorer : Scorer
- {
-
- /* The scorers for subqueries that have remaining docs, kept as a min heap by number of next doc. */
- private System.Collections.ArrayList subScorers = new System.Collections.ArrayList();
-
- /* Multiplier applied to non-maximum-scoring subqueries for a document as they are summed into the result. */
- private float tieBreakerMultiplier;
-
- private bool more = false; // True iff there is a next document
- private bool firstTime = true; // True iff next() has not yet been called
-
- /// <summary>Creates a new instance of DisjunctionMaxScorer</summary>
- /// <param name="tieBreakerMultiplier">Multiplier applied to non-maximum-scoring subqueries for a document as they are summed into the result.
- /// </param>
- /// <param name="similarity">-- not used since our definition involves neither coord nor terms directly
- /// </param>
- public DisjunctionMaxScorer(float tieBreakerMultiplier, Similarity similarity) : base(similarity)
- {
- this.tieBreakerMultiplier = tieBreakerMultiplier;
- }
-
- /// <summary>Add the scorer for a subquery</summary>
- /// <param name="scorer">the scorer of a subquery of our associated DisjunctionMaxQuery
- /// </param>
- public virtual void Add(Scorer scorer)
- {
- if (scorer.Next())
- {
- // Initialize and retain only if it produces docs
- subScorers.Add(scorer);
- more = true;
- }
- }
-
- /// <summary>Generate the next document matching our associated DisjunctionMaxQuery.</summary>
- /// <returns> true iff there is a next document
- /// </returns>
- public override bool Next()
- {
- if (!more)
- return false;
- if (firstTime)
- {
- Heapify();
- firstTime = false;
- return true; // more would have been false if no subScorers had any docs
- }
- // Increment all generators that generated the last doc and adjust the heap.
- int lastdoc = ((Scorer) subScorers[0]).Doc();
- do
- {
- if (((Scorer) subScorers[0]).Next())
- HeapAdjust(0);
- else
- {
- HeapRemoveRoot();
- if ((subScorers.Count == 0))
- return (more = false);
- }
- }
- while (((Scorer) subScorers[0]).Doc() == lastdoc);
- return true;
- }
-
- /// <summary>Determine the current document number. Initially invalid, until {@link #Next()} is called the first time.</summary>
- /// <returns> the document number of the currently generated document
- /// </returns>
- public override int Doc()
- {
- return ((Scorer) subScorers[0]).Doc();
- }
-
- /// <summary>Determine the current document score. Initially invalid, until {@link #Next()} is called the first time.</summary>
- /// <returns> the score of the current generated document
- /// </returns>
- public override float Score()
- {
- int doc = ((Scorer) subScorers[0]).Doc();
- float[] sum = new float[]{((Scorer) subScorers[0]).Score()}, max = new float[]{sum[0]};
- int size = subScorers.Count;
- ScoreAll(1, size, doc, sum, max);
- ScoreAll(2, size, doc, sum, max);
- return max[0] + (sum[0] - max[0]) * tieBreakerMultiplier;
- }
-
- // Recursively iterate all subScorers that generated last doc computing sum and max
- private void ScoreAll(int root, int size, int doc, float[] sum, float[] max)
- {
- if (root < size && ((Scorer) subScorers[root]).Doc() == doc)
- {
- float sub = ((Scorer) subScorers[root]).Score();
- sum[0] += sub;
- max[0] = System.Math.Max(max[0], sub);
- ScoreAll((root << 1) + 1, size, doc, sum, max);
- ScoreAll((root << 1) + 2, size, doc, sum, max);
- }
- }
-
- /// <summary>Advance to the first document beyond the current whose number is greater than or equal to target.</summary>
- /// <param name="target">the minimum number of the next desired document
- /// </param>
- /// <returns> true iff there is a document to be generated whose number is at least target
- /// </returns>
- public override bool SkipTo(int target)
- {
- while (subScorers.Count > 0 && ((Scorer) subScorers[0]).Doc() < target)
- {
- if (((Scorer) subScorers[0]).SkipTo(target))
- HeapAdjust(0);
- else
- HeapRemoveRoot();
- }
- if ((subScorers.Count == 0))
- return (more = false);
- return true;
- }
-
- /// <summary>Explain a score that we computed. UNSUPPORTED -- see explanation capability in DisjunctionMaxQuery.</summary>
- /// <param name="doc">the number of a document we scored
- /// </param>
- /// <returns> the Explanation for our score
- /// </returns>
- public override Explanation Explain(int doc)
- {
- throw new System.NotSupportedException();
- }
-
- // Organize subScorers into a min heap with scorers generating the earlest document on top.
- private void Heapify()
- {
- int size = subScorers.Count;
- for (int i = (size >> 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 = (Scorer) subScorers[root];
- int doc = scorer.Doc();
- int i = root, size = subScorers.Count;
- while (i <= (size >> 1) - 1)
- {
- int lchild = (i << 1) + 1;
- Scorer lscorer = (Scorer) subScorers[lchild];
- int ldoc = lscorer.Doc();
- int rdoc = System.Int32.MaxValue, rchild = (i << 1) + 2;
- Scorer rscorer = null;
- if (rchild < size)
- {
- rscorer = (Scorer) subScorers[rchild];
- rdoc = rscorer.Doc();
- }
- 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()
- {
- int size = subScorers.Count;
- if (size == 1)
- subScorers.RemoveAt(0);
- else
- {
- subScorers[0] = subScorers[size - 1];
- subScorers.RemoveAt(size - 1);
- HeapAdjust(0);
- }
- }
- }
- }