Class FSTCompletionLookup
- java.lang.Object
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- org.apache.lucene.search.suggest.Lookup
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- org.apache.lucene.search.suggest.fst.FSTCompletionLookup
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public class FSTCompletionLookup extends Lookup
An adapter fromLookup
API toFSTCompletion
.This adapter differs from
FSTCompletion
in that it attempts to discretize any "weights" as passed from inTermFreqIterator.weight()
to match the number of buckets. For the rationale for bucketing, seeFSTCompletion
.Note:Discretization requires an additional sorting pass.
The range of weights for bucketing/ discretization is determined by sorting the input by weight and then dividing into equal ranges. Then, scores within each range are assigned to that bucket.
Note that this means that even large differences in weights may be lost during automaton construction, but the overall distinction between "classes" of weights will be preserved regardless of the distribution of weights.
For fine-grained control over which weights are assigned to which buckets, use
FSTCompletion
directly orTSTLookup
, for example.- See Also:
FSTCompletion
- 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
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Fields inherited from class org.apache.lucene.search.suggest.Lookup
CHARSEQUENCE_COMPARATOR
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Constructor Summary
Constructors Constructor Description FSTCompletionLookup()
This constructor prepares for creating a suggested FST using thebuild(TermFreqIterator)
method.FSTCompletionLookup(int buckets, boolean exactMatchFirst)
This constructor prepares for creating a suggested FST using thebuild(TermFreqIterator)
method.FSTCompletionLookup(FSTCompletion completion, boolean exactMatchFirst)
This constructor takes a pre-built automaton.
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Method Summary
All Methods Instance Methods Concrete Methods Modifier and Type Method Description void
build(TermFreqIterator tfit)
Builds up a new internalLookup
representation based on the givenTermFreqIterator
.Object
get(CharSequence key)
boolean
load(InputStream input)
Discard current lookup data and load it from a previously saved copy.List<Lookup.LookupResult>
lookup(CharSequence key, boolean higherWeightsFirst, int num)
Look up a key and return possible completion for this key.boolean
store(OutputStream output)
Persist the constructed lookup data to a directory.
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Constructor Detail
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FSTCompletionLookup
public FSTCompletionLookup()
This constructor prepares for creating a suggested FST using thebuild(TermFreqIterator)
method. The number of weight discretization buckets is set toFSTCompletion.DEFAULT_BUCKETS
and exact matches are promoted to the top of the suggestions list.
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FSTCompletionLookup
public FSTCompletionLookup(int buckets, boolean exactMatchFirst)
This constructor prepares for creating a suggested FST using thebuild(TermFreqIterator)
method.- Parameters:
buckets
- The number of weight discretization buckets (seeFSTCompletion
for details).exactMatchFirst
- Iftrue
exact matches are promoted to the top of the suggestions list. Otherwise they appear in the order of discretized weight and alphabetical within the bucket.
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FSTCompletionLookup
public FSTCompletionLookup(FSTCompletion completion, boolean exactMatchFirst)
This constructor takes a pre-built automaton.- Parameters:
completion
- An instance ofFSTCompletion
.exactMatchFirst
- Iftrue
exact matches are promoted to the top of the suggestions list. Otherwise they appear in the order of discretized weight and alphabetical within the bucket.
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Method Detail
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build
public void build(TermFreqIterator tfit) throws IOException
Builds up a new internalLookup
representation based on the givenTermFreqIterator
. The implementation might re-sort the data internally.- Specified by:
build
in classLookup
- Throws:
IOException
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lookup
public List<Lookup.LookupResult> lookup(CharSequence key, boolean higherWeightsFirst, int num)
Description copied from class:Lookup
Look up a key and return possible completion for this key.- Specified by:
lookup
in classLookup
- Parameters:
key
- lookup key. Depending on the implementation this may be a prefix, misspelling, or even infix.higherWeightsFirst
- 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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get
public Object get(CharSequence key)
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store
public boolean store(OutputStream output) throws IOException
Description copied from class:Lookup
Persist the constructed lookup data to a directory. Optional operation.- Specified by:
store
in classLookup
- Parameters:
output
-OutputStream
to 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(InputStream 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 classLookup
- Parameters:
input
- theInputStream
to 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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