Class CommonGramsFilter

  extended by org.apache.lucene.util.AttributeSource
      extended by org.apache.lucene.analysis.TokenStream
          extended by org.apache.lucene.analysis.TokenFilter
              extended by org.apache.lucene.analysis.commongrams.CommonGramsFilter
All Implemented Interfaces:

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:

Nested Class Summary
Nested classes/interfaces inherited from class org.apache.lucene.util.AttributeSource
AttributeSource.AttributeFactory, AttributeSource.State
Field Summary
static String GRAM_TYPE
Fields inherited from class org.apache.lucene.analysis.TokenFilter
Constructor Summary
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
 boolean incrementToken()
          Inserts bigrams for common words into a token stream.
 void reset()
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
Methods inherited from class java.lang.Object
clone, finalize, getClass, notify, notifyAll, toString, wait, wait, wait

Field Detail


public static final String GRAM_TYPE
See Also:
Constant Field Values
Constructor Detail


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 .

input - TokenStream input in filter chain
commonWords - The set of common words.
Method Detail


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


public void reset()
           throws IOException

reset in class TokenFilter

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