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TruncateTokenFilter.cs
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TruncateTokenFilter.cs
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using Lucene.Net.Analysis.TokenAttributes;
namespace Lucene.Net.Analysis.Miscellaneous
{
/*
* 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.
*/
/// <summary>
/// A token filter for truncating the terms into a specific length.
/// Fixed prefix truncation, as a stemming method, produces good results on Turkish language.
/// It is reported that F5, using first 5 characters, produced best results in
/// <a href="http://www.users.muohio.edu/canf/papers/JASIST2008offPrint.pdf">
/// Information Retrieval on Turkish Texts</a>
/// </summary>
public sealed class TruncateTokenFilter : TokenFilter
{
private readonly ICharTermAttribute termAttribute;
private readonly IKeywordAttribute keywordAttr;
private readonly int length;
public TruncateTokenFilter(TokenStream input, int length)
: base(input)
{
if (length < 1)
{
throw new System.ArgumentOutOfRangeException("length parameter must be a positive number: " + length);
}
this.length = length;
this.termAttribute = AddAttribute<ICharTermAttribute>();
this.keywordAttr = AddAttribute<IKeywordAttribute>();
}
public override sealed bool IncrementToken()
{
if (m_input.IncrementToken())
{
if (!keywordAttr.IsKeyword && termAttribute.Length > length)
{
termAttribute.Length = length;
}
return true;
}
else
{
return false;
}
}
}
}