Package org.apache.lucene.analysis.shingle

Class ShingleFilter

  • All Implemented Interfaces:
    java.io.Closeable, java.lang.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 Detail

      • DEFAULT_FILLER_TOKEN

        public static final java.lang.String DEFAULT_FILLER_TOKEN
        filler token for when positionIncrement is more than 1
        See Also:
        Constant Field Values

      • DEFAULT_MAX_SHINGLE_SIZE

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

      • DEFAULT_MIN_SHINGLE_SIZE

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

      • DEFAULT_TOKEN_TYPE

        public static final java.lang.String DEFAULT_TOKEN_TYPE
        default token type attribute value is "shingle"
        See Also:
        Constant Field Values

      • DEFAULT_TOKEN_SEPARATOR

        public static final java.lang.String DEFAULT_TOKEN_SEPARATOR
        The default string to use when joining adjacent tokens to form a shingle
        See Also:
        Constant Field Values

      • inputWindow

        private java.util.LinkedList<ShingleFilter.InputWindowToken> inputWindow
        The sequence of input stream tokens (or filler tokens, if necessary) that will be composed to form output shingles.

      • gramBuilder

        private java.lang.StringBuilder gramBuilder
        Shingle and unigram text is composed here.

      • tokenType

        private java.lang.String tokenType
        The token type attribute value to use - default is "shingle"

      • tokenSeparator

        private java.lang.String tokenSeparator
        The string to use when joining adjacent tokens to form a shingle

      • fillerToken

        private char[] fillerToken
        The string to insert for each position at which there is no token (i.e., when position increment is greater than one).

      • outputUnigrams

        private boolean outputUnigrams
        By default, we output unigrams (individual tokens) as well as shingles (token n-grams).

      • outputUnigramsIfNoShingles

        private boolean outputUnigramsIfNoShingles
        By default, we don't override behavior of outputUnigrams.

      • maxShingleSize

        private int maxShingleSize
        maximum shingle size (number of tokens)

      • minShingleSize

        private int minShingleSize
        minimum shingle size (number of tokens)

      • numFillerTokensToInsert

        private int numFillerTokensToInsert
        The remaining number of filler tokens to be inserted into the input stream from which shingles are composed, to handle position increments greater than one.

      • nextInputStreamToken

        private AttributeSource nextInputStreamToken
        When the next input stream token has a position increment greater than one, it is stored in this field until sufficient filler tokens have been inserted to account for the position increment.

      • isNextInputStreamToken

        private boolean isNextInputStreamToken
        Whether or not there is a next input stream token.

      • isOutputHere

        private boolean isOutputHere
        Whether at least one unigram or shingle has been output at the current position.

      • noShingleOutput

        boolean noShingleOutput
        true if no shingles have been output yet (for outputUnigramsIfNoShingles).

      • endState

        private AttributeSource.State endState
        Holds the State after input.end() was called, so we can restore it in our end() impl.

      • exhausted

        private boolean exhausted

    • Constructor Detail

      • 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,
                     java.lang.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 Detail

      • setTokenType

        public void setTokenType​(java.lang.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​(java.lang.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​(java.lang.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 java.io.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:
        java.io.IOException

      • getNextToken

        private ShingleFilter.InputWindowToken getNextToken​(ShingleFilter.InputWindowToken target)
                                             throws java.io.IOException

        Get the next token from the input stream.

        If the next token has positionIncrement > 1, positionIncrement - 1 fillerTokens are inserted first.

        Parameters:
        target - Where to put the new token; if null, a new instance is created.
        Returns:
        On success, the populated token; null otherwise
        Throws:
        java.io.IOException - if the input stream has a problem

      • end

        public void end()
         throws java.io.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:
        java.io.IOException - If an I/O error occurs

      • shiftInputWindow

        private void shiftInputWindow()
                       throws java.io.IOException

        Fills inputWindow with input stream tokens, if available, shifting to the right if the window was previously full.

        Resets gramSize to its minimum value.

        Throws:
        java.io.IOException - if there's a problem getting the next token

      • reset

        public void reset()
           throws java.io.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:
        java.io.IOException