pylucene 3.5.0-3

[pylucene.git] / lucene-java-3.5.0 / lucene / src / java / org / apache / lucene / search / NGramPhraseQuery.java

diff --git a/lucene-java-3.5.0/lucene/src/java/org/apache/lucene/search/NGramPhraseQuery.java b/lucene-java-3.5.0/lucene/src/java/org/apache/lucene/search/NGramPhraseQuery.java
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+package org.apache.lucene.search;
+
+/**
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF 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.
+ */
+
+import java.io.IOException;
+
+import org.apache.lucene.index.IndexReader;
+import org.apache.lucene.index.Term;
+
+/**
+ * This is a {@link PhraseQuery} which is optimized for n-gram phrase query.
+ * For example, when you query "ABCD" on a 2-gram field, you may want to use
+ * NGramPhraseQuery rather than {@link PhraseQuery}, because NGramPhraseQuery
+ * will {@link #rewrite(IndexReader)} the query to "AB/0 CD/2", while {@link PhraseQuery}
+ * will query "AB/0 BC/1 CD/2" (where term/position).
+ *
+ */
+public class NGramPhraseQuery extends PhraseQuery {
+  private final int n;
+  
+  /**
+   * Constructor that takes gram size.
+   * @param n
+   */
+  public NGramPhraseQuery(int n){
+    super();
+    this.n = n;
+  }
+
+  @Override
+  public Query rewrite(IndexReader reader) throws IOException {
+    if(getSlop() != 0) return super.rewrite(reader);
+    
+    // check whether optimizable or not
+    if(n < 2 || // non-overlap n-gram cannot be optimized
+        getTerms().length < 3)  // too short to optimize
+      return super.rewrite(reader);
+
+    // check all posIncrement is 1
+    // if not, cannot optimize
+    int[] positions = getPositions();
+    Term[] terms = getTerms();
+    int prevPosition = positions[0];
+    for(int i = 1; i < positions.length; i++){
+      int pos = positions[i];
+      if(prevPosition + 1 != pos) return super.rewrite(reader);
+      prevPosition = pos;
+    }
+
+    // now create the new optimized phrase query for n-gram
+    PhraseQuery optimized = new PhraseQuery();
+    int pos = 0;
+    final int lastPos = terms.length - 1;
+    for(int i = 0; i < terms.length; i++){
+      if(pos % n == 0 || pos >= lastPos){
+        optimized.add(terms[i], positions[i]);
+      }
+      pos++;
+    }
+    
+    return optimized;
+  }
+
+  /** Returns true iff <code>o</code> is equal to this. */
+  @Override
+  public boolean equals(Object o) {
+    if (!(o instanceof NGramPhraseQuery))
+      return false;
+    NGramPhraseQuery other = (NGramPhraseQuery)o;
+    if(this.n != other.n) return false;
+    return super.equals(other);
+  }
+
+  /** Returns a hash code value for this object.*/
+  @Override
+  public int hashCode() {
+    return Float.floatToIntBits(getBoost())
+      ^ getSlop()
+      ^ getTerms().hashCode()
+      ^ getPositions().hashCode()
+      ^ n;
+  }
+}