Package org.apache.lucene.search.suggest.analyzing

Class FreeTextSuggester

  • All Implemented Interfaces:
    Accountable
    public class FreeTextSuggester
extends Lookup
    Builds an ngram model from the text sent to build(org.apache.lucene.search.suggest.InputIterator) and predicts based on the last grams-1 tokens in the request sent to lookup(java.lang.CharSequence, boolean, int). This tries to handle the "long tail" of suggestions for when the incoming query is a never before seen query string.

    Likely this suggester would only be used as a fallback, when the primary suggester fails to find any suggestions.

    Note that the weight for each suggestion is unused, and the suggestions are the analyzed forms (so your analysis process should normally be very "light").

    This uses the stupid backoff language model to smooth scores across ngram models; see "Large language models in machine translation", http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.76.1126 for details.

    From lookup(java.lang.CharSequence, boolean, int), the key of each result is the ngram token; the value is Long.MAX_VALUE * score (fixed point, cast to long). Divide by Long.MAX_VALUE to get the score back, which ranges from 0.0 to 1.0.

    onlyMorePopular is unused.

    WARNING: This API is experimental and might change in incompatible ways in the next release.

    • Field Detail

      • VERSION_START

        public static final int VERSION_START
        Initial version of the saved model file format.
        See Also:
        Constant Field Values

      • VERSION_CURRENT

        public static final int VERSION_CURRENT
        Current version of the saved model file format.
        See Also:
        Constant Field Values

      • DEFAULT_GRAMS

        public static final int DEFAULT_GRAMS
        By default we use a bigram model.
        See Also:
        Constant Field Values

      • ALPHA

        public static final double ALPHA
        The constant used for backoff smoothing; during lookup, this means that if a given trigram did not occur, and we backoff to the bigram, the overall score will be 0.4 times what the bigram model would have assigned.
        See Also:
        Constant Field Values

      • DEFAULT_SEPARATOR

        public static final byte DEFAULT_SEPARATOR
        The default character used to join multiple tokens into a single ngram token. The input tokens produced by the analyzer must not contain this character.
        See Also:
        Constant Field Values

    • Constructor Detail

      • FreeTextSuggester

        public FreeTextSuggester​(Analyzer analyzer)
        Instantiate, using the provided analyzer for both indexing and lookup, using bigram model by default.

      • FreeTextSuggester

        public FreeTextSuggester​(Analyzer indexAnalyzer,
                         Analyzer queryAnalyzer)
        Instantiate, using the provided indexing and lookup analyzers, using bigram model by default.

      • FreeTextSuggester

        public FreeTextSuggester​(Analyzer indexAnalyzer,
                         Analyzer queryAnalyzer,
                         int grams)
        Instantiate, using the provided indexing and lookup analyzers, with the specified model (2 = bigram, 3 = trigram, etc.).

      • FreeTextSuggester

        public FreeTextSuggester​(Analyzer indexAnalyzer,
                         Analyzer queryAnalyzer,
                         int grams,
                         byte separator)
        Instantiate, using the provided indexing and lookup analyzers, and specified model (2 = bigram, 3 = trigram ,etc.). The separator is passed to ShingleFilter.setTokenSeparator(java.lang.String) to join multiple tokens into a single ngram token; it must be an ascii (7-bit-clean) byte. No input tokens should have this byte, otherwise IllegalArgumentException is thrown.

    • Method Detail

      • ramBytesUsed

        public long ramBytesUsed()
        Returns byte size of the underlying FST.

      • build

        public void build​(InputIterator iterator,
                  double ramBufferSizeMB)
           throws IOException
        Build the suggest index, using up to the specified amount of temporary RAM while building. Note that the weights for the suggestions are ignored.
        Throws:
        IOException

      • store

        public boolean store​(DataOutput output)
              throws IOException
        Description copied from class: Lookup
        Persist the constructed lookup data to a directory. Optional operation.
        Specified by:
        store in class Lookup
        Parameters:
        output - DataOutput to write the data to.
        Returns:
        true if successful, false if unsuccessful or not supported.
        Throws:
        IOException - when fatal IO error occurs.

      • load

        public boolean load​(DataInput input)
             throws IOException
        Description copied from class: Lookup
        Discard current lookup data and load it from a previously saved copy. Optional operation.
        Specified by:
        load in class Lookup
        Parameters:
        input - the DataInput to load the lookup data.
        Returns:
        true if completed successfully, false if unsuccessful or not supported.
        Throws:
        IOException - when fatal IO error occurs.

      • lookup

        public List<Lookup.LookupResult> lookup​(CharSequence key,
                                        boolean onlyMorePopular,
                                        int num)
        Description copied from class: Lookup
        Look up a key and return possible completion for this key.
        Overrides:
        lookup in class Lookup
        Parameters:
        key - lookup key. Depending on the implementation this may be a prefix, misspelling, or even infix.
        onlyMorePopular - return only more popular results
        num - maximum number of results to return
        Returns:
        a list of possible completions, with their relative weight (e.g. popularity)

      • lookup

        public List<Lookup.LookupResult> lookup​(CharSequence key,
                                        Set<BytesRef> contexts,
                                        boolean onlyMorePopular,
                                        int num)
        Description copied from class: Lookup
        Look up a key and return possible completion for this key.
        Specified by:
        lookup in class Lookup
        Parameters:
        key - lookup key. Depending on the implementation this may be a prefix, misspelling, or even infix.
        contexts - contexts to filter the lookup by, or null if all contexts are allowed; if the suggestion contains any of the contexts, it's a match
        onlyMorePopular - return only more popular results
        num - maximum number of results to return
        Returns:
        a list of possible completions, with their relative weight (e.g. popularity)

      • getCount

        public long getCount()
        Description copied from class: Lookup
        Get the number of entries the lookup was built with
        Specified by:
        getCount in class Lookup
        Returns:
        total number of suggester entries

      • get

        public Object get​(CharSequence key)
        Returns the weight associated with an input string, or null if it does not exist.