Class FixedShingleFilter

  • All Implemented Interfaces:
    java.io.Closeable, java.lang.AutoCloseable, Unwrappable<TokenStream>

    public final class FixedShingleFilter
    extends GraphTokenFilter
    A FixedShingleFilter constructs shingles (token n-grams) from a token stream. In other words, it creates combinations of tokens as a single token.

    Unlike the ShingleFilter, FixedShingleFilter only emits shingles of a fixed size, and never emits unigrams, even at the end of a TokenStream. In addition, if the filter encounters stacked tokens (eg synonyms), then it will output stacked shingles

    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 "_").

    • Constructor Detail

      • FixedShingleFilter

        public FixedShingleFilter​(TokenStream input,
                                  int shingleSize)
        Creates a FixedShingleFilter over an input token stream
        Parameters:
        input - the input stream
        shingleSize - the shingle size
      • FixedShingleFilter

        public FixedShingleFilter​(TokenStream input,
                                  int shingleSize,
                                  java.lang.String tokenSeparator,
                                  java.lang.String fillerToken)
        Creates a FixedShingleFilter over an input token stream
        Parameters:
        input - the input tokenstream
        shingleSize - the shingle size
        tokenSeparator - a String to use as a token separator
        fillerToken - a String to use to represent gaps in the input stream (due to eg stopwords)
    • Method Detail

      • 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