Class FuzzySuggester

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 Lucene.Net.Util.Automaton.LevenshteinAutomata.MAXIMUM_SUPPORTED_DISTANCE edits. Higher distances are not supported. Note that the fuzzy distance is measured in "byte space" on the bytes returned by the Lucene.Net.Analysis.TokenStream's Lucene.Net.Analysis.TokenAttributes.ITermToBytesRefAttribute, 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 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.

Note

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

Inheritance
object
Lookup
AnalyzingSuggester
FuzzySuggester
Inherited Members
Namespace: Lucene.Net.Search.Suggest.Analyzing
Assembly: Lucene.Net.Suggest.dll
Syntax
public sealed class FuzzySuggester : AnalyzingSuggester

Constructors

FuzzySuggester(Analyzer)

Creates a FuzzySuggester instance initialized with default values.

Declaration
public FuzzySuggester(Analyzer analyzer)
Parameters
Type Name Description
Analyzer analyzer

The Lucene.Net.Analysis.Analyzer used for this suggester.

FuzzySuggester(Analyzer, Analyzer)

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

Declaration
public FuzzySuggester(Analyzer indexAnalyzer, Analyzer queryAnalyzer)
Parameters
Type Name Description
Analyzer indexAnalyzer

Lucene.Net.Analysis.Analyzer that will be used for analyzing suggestions while building the index.
Analyzer queryAnalyzer

Lucene.Net.Analysis.Analyzer that will be used for analyzing query text during lookup

FuzzySuggester(Analyzer, Analyzer, SuggesterOptions, int, int, bool, int, bool, int, int, bool)

Creates a FuzzySuggester instance.

Declaration
public FuzzySuggester(Analyzer indexAnalyzer, Analyzer queryAnalyzer, SuggesterOptions options, int maxSurfaceFormsPerAnalyzedForm, int maxGraphExpansions, bool preservePositionIncrements, int maxEdits, bool transpositions, int nonFuzzyPrefix, int minFuzzyLength, bool unicodeAware)
Parameters
Type Name Description
Analyzer indexAnalyzer

The Lucene.Net.Analysis.Analyzer that will be used for analyzing suggestions while building the index.
Analyzer queryAnalyzer

The Lucene.Net.Analysis.Analyzer that will be used for analyzing query text during lookup
SuggesterOptions options

see EXACT_FIRST, PRESERVE_SEP
int 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.
int maxGraphExpansions

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

Whether position holes should appear in the automaton
int maxEdits

must be >= 0 and <= Lucene.Net.Util.Automaton.LevenshteinAutomata.MAXIMUM_SUPPORTED_DISTANCE.
bool transpositions

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

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

minimum length of lookup key before any edits are allowed (see default DEFAULT_MIN_FUZZY_LENGTH)
bool unicodeAware

operate Unicode code points instead of bytes.

Fields

DEFAULT_MAX_EDITS

The default maximum number of edits for fuzzy suggestions.

Declaration
public const int DEFAULT_MAX_EDITS = 1
Field Value
Type Description
int

DEFAULT_MIN_FUZZY_LENGTH

The default minimum length of the key passed to Lookup before any edits are allowed.

Declaration
public const int DEFAULT_MIN_FUZZY_LENGTH = 3
Field Value
Type Description
int

DEFAULT_NON_FUZZY_PREFIX

The default prefix length where edits are not allowed.

Declaration
public const int DEFAULT_NON_FUZZY_PREFIX = 1
Field Value
Type Description
int

DEFAULT_TRANSPOSITIONS

The default transposition value passed to Lucene.Net.Util.Automaton.LevenshteinAutomata

Declaration
public const bool DEFAULT_TRANSPOSITIONS = true
Field Value
Type Description
bool

DEFAULT_UNICODE_AWARE

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

Declaration
public const bool DEFAULT_UNICODE_AWARE = false
Field Value
Type Description
bool

Methods

ConvertAutomaton(Automaton)

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

Declaration
protected override Automaton ConvertAutomaton(Automaton a)
Parameters
Type Name Description
Automaton a
Returns
Type Description
Automaton
Overrides

GetFullPrefixPaths(IList<Path<Pair>>, Automaton, FST<Pair>)

Returns all prefix paths to initialize the search.

Declaration
protected override IList<FSTUtil.Path<PairOutputs<Int64, BytesRef>.Pair>> GetFullPrefixPaths(IList<FSTUtil.Path<PairOutputs<Int64, BytesRef>.Pair>> prefixPaths, Automaton lookupAutomaton, FST<PairOutputs<Int64, BytesRef>.Pair> fst)
Parameters
Type Name Description
IList<FSTUtil.Path<PairOutputs<Int64, BytesRef>.Pair>> prefixPaths
Automaton lookupAutomaton
FST<PairOutputs<Int64, BytesRef>.Pair> fst
Returns
Type Description
IList<FSTUtil.Path<PairOutputs<Int64, BytesRef>.Pair>>
Overrides