Class CommonGramsFilter

Construct bigrams for frequently occurring terms while indexing. Single terms are still indexed too, with bigrams overlaid. This is achieved through the use of PositionIncrement. 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"

Inheritance
System.Object
AttributeSource
TokenStream
TokenFilter
CommonGramsFilter
Inherited Members
System.Object.Equals(System.Object, System.Object)
System.Object.ReferenceEquals(System.Object, System.Object)
System.Object.GetType()
System.Object.MemberwiseClone()
Assembly: Lucene.Net.Analysis.Common.dll
Syntax
[Serializable]
public sealed class CommonGramsFilter : TokenFilter, IDisposable

Constructors

Name Description
CommonGramsFilter(LuceneVersion, TokenStream, CharArraySet)

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 .

Fields

Name Description
GRAM_TYPE

Methods

Name Description
IncrementToken()

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.
Reset()

This method is called by a consumer before it begins consumption using 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 base.Reset(), otherwise some internal state will not be correctly reset (e.g., Tokenizer will throw System.InvalidOperationException on further usage).

Extension Methods