Class CommonGramsFilter
- java.lang.Object
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- org.apache.lucene.util.AttributeSource
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- org.apache.lucene.analysis.TokenStream
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- org.apache.lucene.analysis.TokenFilter
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- org.apache.lucene.analysis.commongrams.CommonGramsFilter
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- All Implemented Interfaces:
java.io.Closeable
,java.lang.AutoCloseable
public final class CommonGramsFilter extends TokenFilter
Construct bigrams for frequently occurring terms while indexing. Single terms are still indexed too, with bigrams overlaid. This is achieved through the use ofPositionIncrementAttribute.setPositionIncrement(int)
. Bigrams have a type ofGRAM_TYPE
Example:- input:"the quick brown fox"
- output:|"the","the-quick"|"brown"|"fox"|
- "the-quick" has a position increment of 0 so it is in the same position as "the" "the-quick" has a term.type() of "gram"
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Nested Class Summary
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Nested classes/interfaces inherited from class org.apache.lucene.util.AttributeSource
AttributeSource.AttributeFactory, AttributeSource.State
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Field Summary
Fields Modifier and Type Field Description static java.lang.String
GRAM_TYPE
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Constructor Summary
Constructors Constructor Description CommonGramsFilter(Version matchVersion, TokenStream input, CharArraySet commonWords)
Construct a token stream filtering the given input using a Set of common words to create bigrams.
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Method Summary
All Methods Instance Methods Concrete Methods Modifier and Type Method Description boolean
incrementToken()
Inserts bigrams for common words into a token stream.void
reset()
This method is called by a consumer before it begins consumption usingTokenStream.incrementToken()
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Methods inherited from class org.apache.lucene.analysis.TokenFilter
close, end
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Methods inherited from class org.apache.lucene.util.AttributeSource
addAttribute, addAttributeImpl, captureState, clearAttributes, cloneAttributes, copyTo, equals, getAttribute, getAttributeClassesIterator, getAttributeFactory, getAttributeImplsIterator, hasAttribute, hasAttributes, hashCode, reflectAsString, reflectWith, restoreState, toString
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Field Detail
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GRAM_TYPE
public static final java.lang.String GRAM_TYPE
- See Also:
- Constant Field Values
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Constructor Detail
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CommonGramsFilter
public CommonGramsFilter(Version matchVersion, TokenStream input, CharArraySet commonWords)
Construct a token stream filtering the given input using a Set of common words to create bigrams. Outputs both unigrams with position increment and bigrams with position increment 0 type=gram where one or both of the words in a potential bigram are in the set of common words .- Parameters:
input
- TokenStream input in filter chaincommonWords
- The set of common words.
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Method Detail
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incrementToken
public boolean incrementToken() throws java.io.IOException
Inserts bigrams for common words into a token stream. For each input token, output the token. If the token and/or the following token are in the list of common words also output a bigram with position increment 0 and type="gram" TODO:Consider adding an option to not emit unigram stopwords as in CDL XTF BigramStopFilter, CommonGramsQueryFilter would need to be changed to work with this. TODO: Consider optimizing for the case of three commongrams i.e "man of the year" normally produces 3 bigrams: "man-of", "of-the", "the-year" but with proper management of positions we could eliminate the middle bigram "of-the"and save a disk seek and a whole set of position lookups.- Specified by:
incrementToken
in classTokenStream
- Returns:
- false for end of stream; true otherwise
- Throws:
java.io.IOException
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reset
public void reset() throws java.io.IOException
This method is called by a consumer before it begins consumption usingTokenStream.incrementToken()
.Resets this stream to a clean state. Stateful implementations must implement this method so that they can be reused, just as if they had been created fresh.
If you override this method, always call
super.reset()
, otherwise some internal state will not be correctly reset (e.g.,Tokenizer
will throwIllegalStateException
on further usage).NOTE: The default implementation chains the call to the input TokenStream, so be sure to call
super.reset()
when overriding this method.- Overrides:
reset
in classTokenFilter
- Throws:
java.io.IOException
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