Class FreeTextSuggester
- java.lang.Object
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- org.apache.lucene.search.suggest.Lookup
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- org.apache.lucene.search.suggest.analyzing.FreeTextSuggester
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- All Implemented Interfaces:
Accountable
public class FreeTextSuggester extends Lookup
Builds an ngram model from the text sent tobuild(org.apache.lucene.search.suggest.InputIterator)and predicts based on the last grams-1 tokens in the request sent tolookup(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.
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Nested Class Summary
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Nested classes/interfaces inherited from class org.apache.lucene.search.suggest.Lookup
Lookup.LookupPriorityQueue, Lookup.LookupResult
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Field Summary
Fields Modifier and Type Field Description static doubleALPHAThe 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.static StringCODEC_NAMECodec name used in the header for the saved model.static intDEFAULT_GRAMSBy default we use a bigram model.static byteDEFAULT_SEPARATORThe default character used to join multiple tokens into a single ngram token.static intVERSION_CURRENTCurrent version of the saved model file format.static intVERSION_STARTInitial version of the saved model file format.-
Fields inherited from class org.apache.lucene.search.suggest.Lookup
CHARSEQUENCE_COMPARATOR
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Fields inherited from interface org.apache.lucene.util.Accountable
NULL_ACCOUNTABLE
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Constructor Summary
Constructors Constructor Description FreeTextSuggester(Analyzer analyzer)Instantiate, using the provided analyzer for both indexing and lookup, using bigram model by default.FreeTextSuggester(Analyzer indexAnalyzer, Analyzer queryAnalyzer)Instantiate, using the provided indexing and lookup analyzers, using bigram model by default.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(Analyzer indexAnalyzer, Analyzer queryAnalyzer, int grams, byte separator)Instantiate, using the provided indexing and lookup analyzers, and specified model (2 = bigram, 3 = trigram ,etc.).
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Method Summary
All Methods Instance Methods Concrete Methods Modifier and Type Method Description voidbuild(InputIterator iterator)Builds up a new internalLookuprepresentation based on the givenInputIterator.voidbuild(InputIterator iterator, double ramBufferSizeMB)Build the suggest index, using up to the specified amount of temporary RAM while building.Objectget(CharSequence key)Returns the weight associated with an input string, or null if it does not exist.Collection<Accountable>getChildResources()longgetCount()Get the number of entries the lookup was built withbooleanload(DataInput input)Discard current lookup data and load it from a previously saved copy.List<Lookup.LookupResult>lookup(CharSequence key, boolean onlyMorePopular, int num)Look up a key and return possible completion for this key.List<Lookup.LookupResult>lookup(CharSequence key, int num)Lookup, without any context.List<Lookup.LookupResult>lookup(CharSequence key, Set<BytesRef> contexts, boolean onlyMorePopular, int num)Look up a key and return possible completion for this key.List<Lookup.LookupResult>lookup(CharSequence key, Set<BytesRef> contexts, int num)Retrieve suggestions.longramBytesUsed()Returns byte size of the underlying FST.booleanstore(DataOutput output)Persist the constructed lookup data to a directory.
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Field Detail
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CODEC_NAME
public static final String CODEC_NAME
Codec name used in the header for the saved model.- See Also:
- Constant Field Values
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VERSION_START
public static final int VERSION_START
Initial version of the saved model file format.- See Also:
- Constant Field Values
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VERSION_CURRENT
public static final int VERSION_CURRENT
Current version of the saved model file format.- See Also:
- Constant Field Values
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DEFAULT_GRAMS
public static final int DEFAULT_GRAMS
By default we use a bigram model.- See Also:
- Constant Field Values
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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
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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
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Constructor Detail
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FreeTextSuggester
public FreeTextSuggester(Analyzer analyzer)
Instantiate, using the provided analyzer for both indexing and lookup, using bigram model by default.
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FreeTextSuggester
public FreeTextSuggester(Analyzer indexAnalyzer, Analyzer queryAnalyzer)
Instantiate, using the provided indexing and lookup analyzers, using bigram model by default.
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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.).
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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 toShingleFilter.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, otherwiseIllegalArgumentExceptionis thrown.
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Method Detail
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ramBytesUsed
public long ramBytesUsed()
Returns byte size of the underlying FST.
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getChildResources
public Collection<Accountable> getChildResources()
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build
public void build(InputIterator iterator) throws IOException
Description copied from class:LookupBuilds up a new internalLookuprepresentation based on the givenInputIterator. The implementation might re-sort the data internally.- Specified by:
buildin classLookup- Throws:
IOException
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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
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store
public boolean store(DataOutput output) throws IOException
Description copied from class:LookupPersist the constructed lookup data to a directory. Optional operation.- Specified by:
storein classLookup- Parameters:
output-DataOutputto write the data to.- Returns:
- true if successful, false if unsuccessful or not supported.
- Throws:
IOException- when fatal IO error occurs.
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load
public boolean load(DataInput input) throws IOException
Description copied from class:LookupDiscard current lookup data and load it from a previously saved copy. Optional operation.- Specified by:
loadin classLookup- Parameters:
input- theDataInputto load the lookup data.- Returns:
- true if completed successfully, false if unsuccessful or not supported.
- Throws:
IOException- when fatal IO error occurs.
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lookup
public List<Lookup.LookupResult> lookup(CharSequence key, boolean onlyMorePopular, int num)
Description copied from class:LookupLook up a key and return possible completion for this key.- Overrides:
lookupin classLookup- Parameters:
key- lookup key. Depending on the implementation this may be a prefix, misspelling, or even infix.onlyMorePopular- return only more popular resultsnum- maximum number of results to return- Returns:
- a list of possible completions, with their relative weight (e.g. popularity)
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lookup
public List<Lookup.LookupResult> lookup(CharSequence key, int num)
Lookup, without any context.
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lookup
public List<Lookup.LookupResult> lookup(CharSequence key, Set<BytesRef> contexts, boolean onlyMorePopular, int num)
Description copied from class:LookupLook up a key and return possible completion for this key.- Specified by:
lookupin classLookup- 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 matchonlyMorePopular- return only more popular resultsnum- maximum number of results to return- Returns:
- a list of possible completions, with their relative weight (e.g. popularity)
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getCount
public long getCount()
Description copied from class:LookupGet the number of entries the lookup was built with
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lookup
public List<Lookup.LookupResult> lookup(CharSequence key, Set<BytesRef> contexts, int num) throws IOException
Retrieve suggestions.- Throws:
IOException
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get
public Object get(CharSequence key)
Returns the weight associated with an input string, or null if it does not exist.
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