org.apache.lucene.analysis.commongrams

Class CommonGramsFilter

java.lang.Object

org.apache.lucene.util.AttributeSource

org.apache.lucene.analysis.TokenStream

org.apache.lucene.analysis.TokenFilter

org.apache.lucene.analysis.commongrams.CommonGramsFilter

All Implemented Interfaces:

Closeable, 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 of PositionIncrementAttribute.setPositionIncrement(int). Bigrams have a type of GRAM_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"

Nested Class Summary

Nested classes/interfaces inherited from class org.apache.lucene.util.AttributeSource

AttributeSource.AttributeFactory, AttributeSource.State

Field Summary

Fields

Modifier and Type	Field and Description
static String	GRAM_TYPE

Constructor Summary

Constructors

Constructor and 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.

Method Summary

Modifier and Type	Method and 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 using TokenStream.incrementToken().

Methods inherited from class org.apache.lucene.analysis.TokenFilter

close, end

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

Methods inherited from class java.lang.Object

getClass, notify, notifyAll, wait, wait, wait

Field Detail

GRAM_TYPE

public static final String GRAM_TYPE

See Also:

Constant Field Values

Constructor Detail

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 chain

commonWords - The set of common words.

Method Detail

incrementToken

public boolean incrementToken()
                       throws 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 class TokenStream

Returns:

false for end of stream; true otherwise

Throws:

IOException

reset

public void reset()
           throws IOException

This method is called by a consumer before it begins consumption using TokenStream.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 throw IllegalStateException 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 class TokenFilter

Throws:

IOException