pylucene 3.5.0-3

[pylucene.git] / lucene-java-3.5.0 / lucene / contrib / queries / src / java / org / apache / lucene / search / BoostingQuery.java

diff --git a/lucene-java-3.5.0/lucene/contrib/queries/src/java/org/apache/lucene/search/BoostingQuery.java b/lucene-java-3.5.0/lucene/contrib/queries/src/java/org/apache/lucene/search/BoostingQuery.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.search.BooleanQuery;
+import org.apache.lucene.search.DefaultSimilarity;
+import org.apache.lucene.search.Query;
+import org.apache.lucene.search.Searcher;
+import org.apache.lucene.search.Similarity;
+/**
+ * The BoostingQuery class can be used to effectively demote results that match a given query. 
+ * Unlike the "NOT" clause, this still selects documents that contain undesirable terms, 
+ * but reduces their overall score:
+ *
+ *     Query balancedQuery = new BoostingQuery(positiveQuery, negativeQuery, 0.01f);
+ * In this scenario the positiveQuery contains the mandatory, desirable criteria which is used to 
+ * select all matching documents, and the negativeQuery contains the undesirable elements which 
+ * are simply used to lessen the scores. Documents that match the negativeQuery have their score 
+ * multiplied by the supplied "boost" parameter, so this should be less than 1 to achieve a 
+ * demoting effect
+ * 
+ * This code was originally made available here: [WWW] http://marc.theaimsgroup.com/?l=lucene-user&m=108058407130459&w=2
+ * and is documented here: http://wiki.apache.org/lucene-java/CommunityContributions
+ */
+public class BoostingQuery extends Query {
+    private float boost;                            // the amount to boost by
+    private Query match;                            // query to match
+    private Query context;                          // boost when matches too
+
+    public BoostingQuery(Query match, Query context, float boost) {
+      this.match = match;
+      this.context = (Query)context.clone();        // clone before boost
+      this.boost = boost;
+
+      this.context.setBoost(0.0f);                      // ignore context-only matches
+    }
+
+    @Override
+    public Query rewrite(IndexReader reader) throws IOException {
+      BooleanQuery result = new BooleanQuery() {
+
+        @Override
+        public Similarity getSimilarity(Searcher searcher) {
+          return new DefaultSimilarity() {
+
+            @Override
+            public float coord(int overlap, int max) {
+              switch (overlap) {
+
+              case 1:                               // matched only one clause
+                return 1.0f;                        // use the score as-is
+
+              case 2:                               // matched both clauses
+                return boost;                       // multiply by boost
+
+              default:
+                return 0.0f;
+                
+              }
+            }
+          };
+        }
+      };
+
+      result.add(match, BooleanClause.Occur.MUST);
+      result.add(context, BooleanClause.Occur.SHOULD);
+
+      return result;
+    }
+
+    @Override
+    public int hashCode() {
+      final int prime = 31;
+      int result = 1;
+      result = prime * result + Float.floatToIntBits(boost);
+      result = prime * result + ((context == null) ? 0 : context.hashCode());
+      result = prime * result + ((match == null) ? 0 : match.hashCode());
+      return result;
+    }
+
+    @Override
+    public boolean equals(Object obj) {
+      if (this == obj)
+        return true;
+      if (obj == null)
+        return false;
+      if (getClass() != obj.getClass())
+        return false;
+      BoostingQuery other = (BoostingQuery) obj;
+      if (Float.floatToIntBits(boost) != Float.floatToIntBits(other.boost))
+        return false;
+      if (context == null) {
+        if (other.context != null)
+          return false;
+      } else if (!context.equals(other.context))
+        return false;
+      if (match == null) {
+        if (other.match != null)
+          return false;
+      } else if (!match.equals(other.match))
+        return false;
+      return true;
+    }
+
+    @Override
+    public String toString(String field) {
+      return match.toString(field) + "/" + context.toString(field);
+    }
+  }