SimilarityQueries.cs

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/*
 * 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.
 */

using System;
using System.Collections.Generic;
using Lucene.Net.Analysis;
using Lucene.Net.Index;
using Lucene.Net.Analysis.Tokenattributes;

namespace Lucene.Net.Search.Similar
{

    public sealed class SimilarityQueries
    {
        private SimilarityQueries()
        {
        }

        public static Query FormSimilarQuery(System.String body, Analyzer a, System.String field, ISet<string> stop)
        {
            TokenStream ts = a.TokenStream(field, new System.IO.StringReader(body));
            ITermAttribute termAtt = ts.AddAttribute<ITermAttribute>();

            BooleanQuery tmp = new BooleanQuery();
            ISet<string> already = Lucene.Net.Support.Compatibility.SetFactory.CreateHashSet<string>(); // ignore dups
            while (ts.IncrementToken())
            {
                String word = termAtt.Term;
                // ignore opt stop words
                if (stop != null && stop.Contains(word))
                    continue;
                // ignore dups
                if (already.Contains(word))
                    continue;
                already.Add(word);
                // add to query
                TermQuery tq = new TermQuery(new Term(field, word));
                try
                {
                    tmp.Add(tq, Occur.SHOULD);
                }
                catch (BooleanQuery.TooManyClauses)
                {
                    // fail-safe, just return what we have, not the end of the world
                    break;
                }
            }
            return tmp;
        }
    }
}