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
Implements
System.IDisposable
Inherited Members
System.Object.Equals(System.Object, System.Object)
System.Object.GetType()
System.Object.MemberwiseClone()
System.Object.ReferenceEquals(System.Object, System.Object)
Namespace: Lucene.Net.Analysis.CommonGrams
Assembly: Lucene.Net.Analysis.Common.dll
Syntax
public sealed class CommonGramsFilter : TokenFilter, IDisposable

Constructors

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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 .

Declaration
public CommonGramsFilter(LuceneVersion matchVersion, TokenStream input, CharArraySet commonWords)
Parameters
Type Name Description
LuceneVersion matchVersion

lucene compatibility version

TokenStream input

TokenStream input in filter chain

CharArraySet commonWords

The set of common words.

Fields

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GRAM_TYPE

Declaration
public const string GRAM_TYPE = "gram"
Field Value
Type Description
System.String

Methods

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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.

Declaration
public override bool IncrementToken()
Returns
Type Description
System.Boolean
Overrides
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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).

Declaration
public override void Reset()
Overrides
Remarks

NOTE: The default implementation chains the call to the input TokenStream, so be sure to call base.Reset() when overriding this method.

Implements

System.IDisposable