Package org.apache.lucene.analysis.shingle

Class ShingleFilter

java.lang.Object
org.apache.lucene.util.AttributeSource
org.apache.lucene.analysis.TokenStream
org.apache.lucene.analysis.TokenFilter
org.apache.lucene.analysis.shingle.ShingleFilter
All Implemented Interfaces:
Closeable, AutoCloseable
public final class ShingleFilter extends TokenFilter

A ShingleFilter constructs shingles (token n-grams) from a token stream. In other words, it creates combinations of tokens as a single token.

For example, the sentence "please divide this sentence into shingles" might be tokenized into shingles "please divide", "divide this", "this sentence", "sentence into", and "into shingles".

This filter handles position increments > 1 by inserting filler tokens (tokens with termtext "_"). It does not handle a position increment of 0.

  • Field Details

    • DEFAULT_FILLER_TOKEN

      public static final String DEFAULT_FILLER_TOKEN
      filler token for when positionIncrement is more than 1
      See Also:

    • DEFAULT_MAX_SHINGLE_SIZE

      public static final int DEFAULT_MAX_SHINGLE_SIZE
      default maximum shingle size is 2.
      See Also:

    • DEFAULT_MIN_SHINGLE_SIZE

      public static final int DEFAULT_MIN_SHINGLE_SIZE
      default minimum shingle size is 2.
      See Also:

    • DEFAULT_TOKEN_TYPE

      public static final String DEFAULT_TOKEN_TYPE
      default token type attribute value is "shingle"
      See Also:

    • DEFAULT_TOKEN_SEPARATOR

      public static final String DEFAULT_TOKEN_SEPARATOR
      The default string to use when joining adjacent tokens to form a shingle
      See Also:

  • Constructor Details

    • ShingleFilter

      public ShingleFilter(TokenStream input, int minShingleSize, int maxShingleSize)
      Constructs a ShingleFilter with the specified shingle size from the TokenStream input
      Parameters:
      input - input stream
      minShingleSize - minimum shingle size produced by the filter.
      maxShingleSize - maximum shingle size produced by the filter.

    • ShingleFilter

      public ShingleFilter(TokenStream input, int maxShingleSize)
      Constructs a ShingleFilter with the specified shingle size from the TokenStream input
      Parameters:
      input - input stream
      maxShingleSize - maximum shingle size produced by the filter.

    • ShingleFilter

      public ShingleFilter(TokenStream input)
      Construct a ShingleFilter with default shingle size: 2.
      Parameters:
      input - input stream

    • ShingleFilter

      public ShingleFilter(TokenStream input, String tokenType)
      Construct a ShingleFilter with the specified token type for shingle tokens and the default shingle size: 2
      Parameters:
      input - input stream
      tokenType - token type for shingle tokens

  • Method Details

    • setTokenType

      public void setTokenType(String tokenType)
      Set the type of the shingle tokens produced by this filter. (default: "shingle")
      Parameters:
      tokenType - token tokenType

    • setOutputUnigrams

      public void setOutputUnigrams(boolean outputUnigrams)
      Shall the output stream contain the input tokens (unigrams) as well as shingles? (default: true.)
      Parameters:
      outputUnigrams - Whether or not the output stream shall contain the input tokens (unigrams)

    • setOutputUnigramsIfNoShingles

      public void setOutputUnigramsIfNoShingles(boolean outputUnigramsIfNoShingles)

      Shall we override the behavior of outputUnigrams==false for those times when no shingles are available (because there are fewer than minShingleSize tokens in the input stream)? (default: false.)

      Note that if outputUnigrams==true, then unigrams are always output, regardless of whether any shingles are available.

      Parameters:
      outputUnigramsIfNoShingles - Whether or not to output a single unigram when no shingles are available.

    • setMaxShingleSize

      public void setMaxShingleSize(int maxShingleSize)
      Set the max shingle size (default: 2)
      Parameters:
      maxShingleSize - max size of output shingles

    • setMinShingleSize

      public void setMinShingleSize(int minShingleSize)

      Set the min shingle size (default: 2).

      This method requires that the passed in minShingleSize is not greater than maxShingleSize, so make sure that maxShingleSize is set before calling this method.

      The unigram output option is independent of the min shingle size.

      Parameters:
      minShingleSize - min size of output shingles

    • setTokenSeparator

      public void setTokenSeparator(String tokenSeparator)
      Sets the string to use when joining adjacent tokens to form a shingle
      Parameters:
      tokenSeparator - used to separate input stream tokens in output shingles

    • setFillerToken

      public void setFillerToken(String fillerToken)
      Sets the string to insert for each position at which there is no token (i.e., when position increment is greater than one).
      Parameters:
      fillerToken - string to insert at each position where there is no token

    • incrementToken

      public boolean incrementToken() throws IOException
      Description copied from class: TokenStream
      Consumers (i.e., IndexWriter) use this method to advance the stream to the next token. Implementing classes must implement this method and update the appropriate AttributeImpls with the attributes of the next token.

      The producer must make no assumptions about the attributes after the method has been returned: the caller may arbitrarily change it. If the producer needs to preserve the state for subsequent calls, it can use AttributeSource.captureState() to create a copy of the current attribute state.

      This method is called for every token of a document, so an efficient implementation is crucial for good performance. To avoid calls to AttributeSource.addAttribute(Class) and AttributeSource.getAttribute(Class), references to all AttributeImpls that this stream uses should be retrieved during instantiation.

      To ensure that filters and consumers know which attributes are available, the attributes must be added during instantiation. Filters and consumers are not required to check for availability of attributes in TokenStream.incrementToken().

      Specified by:
      incrementToken in class TokenStream
      Returns:
      false for end of stream; true otherwise
      Throws:
      IOException

    • end

      public void end() throws IOException
      Description copied from class: TokenFilter
      This method is called by the consumer after the last token has been consumed, after TokenStream.incrementToken() returned false (using the new TokenStream API). Streams implementing the old API should upgrade to use this feature.

      This method can be used to perform any end-of-stream operations, such as setting the final offset of a stream. The final offset of a stream might differ from the offset of the last token eg in case one or more whitespaces followed after the last token, but a WhitespaceTokenizer was used.

      Additionally any skipped positions (such as those removed by a stopfilter) can be applied to the position increment, or any adjustment of other attributes where the end-of-stream value may be important.

      If you override this method, always call super.end().

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

      Overrides:
      end in class TokenFilter
      Throws:
      IOException - If an I/O error occurs

    • reset

      public void reset() throws IOException
      Description copied from class: TokenFilter
      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