org.apache.lucene.search.suggest.analyzing

Class FuzzySuggester

java.lang.Object

org.apache.lucene.search.suggest.Lookup

org.apache.lucene.search.suggest.analyzing.AnalyzingSuggester

org.apache.lucene.search.suggest.analyzing.FuzzySuggester

public final class FuzzySuggester
extends AnalyzingSuggester

Implements a fuzzy AnalyzingSuggester. The similarity measurement is based on the Damerau-Levenshtein (optimal string alignment) algorithm, though you can explicitly choose classic Levenshtein by passing false for the transpositions parameter.

At most, this query will match terms up to 2 edits. Higher distances are not supported. Note that the fuzzy distance is measured in "byte space" on the bytes returned by the TokenStream's TermToBytesRefAttribute, usually UTF8. By default the analyzed bytes must be at least 3 DEFAULT_MIN_FUZZY_LENGTH bytes before any edits are considered. Furthermore, the first 1 DEFAULT_NON_FUZZY_PREFIX byte is not allowed to be edited. We allow up to 1 (@link #DEFAULT_MAX_EDITS} edit. If unicodeAware parameter in the constructor is set to true, maxEdits, minFuzzyLength, transpositions and nonFuzzyPrefix are measured in Unicode code points (actual letters) instead of bytes.

NOTE: This suggester does not boost suggestions that required no edits over suggestions that did require edits. This is a known limitation.

Note: complex query analyzers can have a significant impact on the lookup performance. It's recommended to not use analyzers that drop or inject terms like synonyms to keep the complexity of the prefix intersection low for good lookup performance. At index time, complex analyzers can safely be used.

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

Nested Class Summary

Nested classes/interfaces inherited from class org.apache.lucene.search.suggest.Lookup

Lookup.LookupPriorityQueue, Lookup.LookupResult

Field Summary

Fields

Modifier and Type	Field and Description
static int	DEFAULT_MAX_EDITS The default maximum number of edits for fuzzy suggestions.
static int	DEFAULT_MIN_FUZZY_LENGTH The default minimum length of the key passed to AnalyzingSuggester.lookup(java.lang.CharSequence, boolean, int) before any edits are allowed.
static int	DEFAULT_NON_FUZZY_PREFIX The default prefix length where edits are not allowed.
static boolean	DEFAULT_TRANSPOSITIONS The default transposition value passed to LevenshteinAutomata
static boolean	DEFAULT_UNICODE_AWARE Measure maxEdits, minFuzzyLength, transpositions and nonFuzzyPrefix parameters in Unicode code points (actual letters) instead of bytes.

Fields inherited from class org.apache.lucene.search.suggest.analyzing.AnalyzingSuggester

EXACT_FIRST, PRESERVE_SEP

Fields inherited from class org.apache.lucene.search.suggest.Lookup

CHARSEQUENCE_COMPARATOR

Constructor Summary

Constructors

Constructor and Description
FuzzySuggester(Analyzer analyzer) Creates a FuzzySuggester instance initialized with default values.
FuzzySuggester(Analyzer indexAnalyzer, Analyzer queryAnalyzer) Creates a FuzzySuggester instance with an index & a query analyzer initialized with default values.
FuzzySuggester(Analyzer indexAnalyzer, Analyzer queryAnalyzer, int options, int maxSurfaceFormsPerAnalyzedForm, int maxGraphExpansions, boolean preservePositionIncrements, int maxEdits, boolean transpositions, int nonFuzzyPrefix, int minFuzzyLength, boolean unicodeAware) Creates a FuzzySuggester instance.

Method Summary

Methods

Modifier and Type	Method and Description
protected Automaton	convertAutomaton(Automaton a) Used by subclass to change the lookup automaton, if necessary.
protected List<FSTUtil.Path<PairOutputs.Pair<Long,BytesRef>>>	getFullPrefixPaths(List<FSTUtil.Path<PairOutputs.Pair<Long,BytesRef>>> prefixPaths, Automaton lookupAutomaton, FST<PairOutputs.Pair<Long,BytesRef>> fst) Returns all prefix paths to initialize the search.

Methods inherited from class org.apache.lucene.search.suggest.analyzing.AnalyzingSuggester

build, get, load, lookup, sizeInBytes, store

Methods inherited from class org.apache.lucene.search.suggest.Lookup

build

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Field Detail

DEFAULT_UNICODE_AWARE

public static final boolean DEFAULT_UNICODE_AWARE

Measure maxEdits, minFuzzyLength, transpositions and nonFuzzyPrefix parameters in Unicode code points (actual letters) instead of bytes.

See Also:

Constant Field Values

DEFAULT_MIN_FUZZY_LENGTH

public static final int DEFAULT_MIN_FUZZY_LENGTH

The default minimum length of the key passed to AnalyzingSuggester.lookup(java.lang.CharSequence, boolean, int) before any edits are allowed.

See Also:

Constant Field Values

DEFAULT_NON_FUZZY_PREFIX

public static final int DEFAULT_NON_FUZZY_PREFIX

The default prefix length where edits are not allowed.

See Also:

Constant Field Values

DEFAULT_MAX_EDITS

public static final int DEFAULT_MAX_EDITS

The default maximum number of edits for fuzzy suggestions.

See Also:

Constant Field Values

DEFAULT_TRANSPOSITIONS

public static final boolean DEFAULT_TRANSPOSITIONS

The default transposition value passed to LevenshteinAutomata

See Also:

Constant Field Values

Constructor Detail

FuzzySuggester

public FuzzySuggester(Analyzer analyzer)

Creates a FuzzySuggester instance initialized with default values.

Parameters:

analyzer - the analyzer used for this suggester

FuzzySuggester

public FuzzySuggester(Analyzer indexAnalyzer,
              Analyzer queryAnalyzer)

Creates a FuzzySuggester instance with an index & a query analyzer initialized with default values.

Parameters:

indexAnalyzer - Analyzer that will be used for analyzing suggestions while building the index.

queryAnalyzer - Analyzer that will be used for analyzing query text during lookup

FuzzySuggester

public FuzzySuggester(Analyzer indexAnalyzer,
              Analyzer queryAnalyzer,
              int options,
              int maxSurfaceFormsPerAnalyzedForm,
              int maxGraphExpansions,
              boolean preservePositionIncrements,
              int maxEdits,
              boolean transpositions,
              int nonFuzzyPrefix,
              int minFuzzyLength,
              boolean unicodeAware)

Creates a FuzzySuggester instance.

Parameters:

indexAnalyzer - Analyzer that will be used for analyzing suggestions while building the index.

queryAnalyzer - Analyzer that will be used for analyzing query text during lookup

options - see AnalyzingSuggester.EXACT_FIRST, AnalyzingSuggester.PRESERVE_SEP

maxSurfaceFormsPerAnalyzedForm - Maximum number of surface forms to keep for a single analyzed form. When there are too many surface forms we discard the lowest weighted ones.

maxGraphExpansions - Maximum number of graph paths to expand from the analyzed form. Set this to -1 for no limit.

preservePositionIncrements - Whether position holes should appear in the automaton

maxEdits - must be >= 0 and <= LevenshteinAutomata.MAXIMUM_SUPPORTED_DISTANCE .

transpositions - true if transpositions should be treated as a primitive edit operation. If this is false, comparisons will implement the classic Levenshtein algorithm.

nonFuzzyPrefix - length of common (non-fuzzy) prefix (see default DEFAULT_NON_FUZZY_PREFIX

minFuzzyLength - minimum length of lookup key before any edits are allowed (see default DEFAULT_MIN_FUZZY_LENGTH)

unicodeAware - operate Unicode code points instead of bytes.

Method Detail

getFullPrefixPaths

protected List<FSTUtil.Path<PairOutputs.Pair<Long,BytesRef>>> getFullPrefixPaths(List<FSTUtil.Path<PairOutputs.Pair<Long,BytesRef>>> prefixPaths,
                                                                     Automaton lookupAutomaton,
                                                                     FST<PairOutputs.Pair<Long,BytesRef>> fst)
                                                                          throws IOException

Description copied from class: AnalyzingSuggester

Returns all prefix paths to initialize the search.

Overrides:

getFullPrefixPaths in class AnalyzingSuggester

Throws:

IOException

convertAutomaton

protected Automaton convertAutomaton(Automaton a)

Description copied from class: AnalyzingSuggester

Used by subclass to change the lookup automaton, if necessary.

Overrides:

convertAutomaton in class AnalyzingSuggester