org.apache.lucene.search

Class FuzzyQuery

java.lang.Object

org.apache.lucene.search.Query

org.apache.lucene.search.MultiTermQuery

org.apache.lucene.search.FuzzyQuery

public class FuzzyQuery
extends MultiTermQuery

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

This query uses MultiTermQuery.TopTermsBlendedFreqScoringRewrite as default. So terms will be collected and scored according to their edit distance. Only the top terms are used for building the BooleanQuery. It is not recommended to change the rewrite mode for fuzzy queries.

At most, this query will match terms up to 2 edits. Higher distances (especially with transpositions enabled), are generally not useful and will match a significant amount of the term dictionary. If you really want this, consider using an n-gram indexing technique (such as the SpellChecker in the suggest module) instead.

NOTE: terms of length 1 or 2 will sometimes not match because of how the scaled distance between two terms is computed. For a term to match, the edit distance between the terms must be less than the minimum length term (either the input term, or the candidate term). For example, FuzzyQuery on term "abcd" with maxEdits=2 will not match an indexed term "ab", and FuzzyQuery on term "a" with maxEdits=2 will not match an indexed term "abc".

Nested Class Summary

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

MultiTermQuery.RewriteMethod, MultiTermQuery.TopTermsBlendedFreqScoringRewrite, MultiTermQuery.TopTermsBoostOnlyBooleanQueryRewrite, MultiTermQuery.TopTermsScoringBooleanQueryRewrite

Field Summary

Fields

Modifier and Type	Field and Description
static int	defaultMaxEdits
static int	defaultMaxExpansions
static float	defaultMinSimilarity Deprecated. pass integer edit distances instead.
static int	defaultPrefixLength
static boolean	defaultTranspositions

Fields inherited from class org.apache.lucene.search.MultiTermQuery

CONSTANT_SCORE_BOOLEAN_REWRITE, CONSTANT_SCORE_REWRITE, field, rewriteMethod, SCORING_BOOLEAN_REWRITE

Constructor Summary

Constructors

Constructor and Description
FuzzyQuery(Term term) Calls FuzzyQuery(term, defaultMaxEdits).
FuzzyQuery(Term term, int maxEdits) Calls FuzzyQuery(term, maxEdits, defaultPrefixLength).
FuzzyQuery(Term term, int maxEdits, int prefixLength) Calls FuzzyQuery(term, maxEdits, prefixLength, defaultMaxExpansions, defaultTranspositions).
FuzzyQuery(Term term, int maxEdits, int prefixLength, int maxExpansions, boolean transpositions) Create a new FuzzyQuery that will match terms with an edit distance of at most maxEdits to term.

Method Summary

Modifier and Type	Method and Description
boolean	equals(Object obj) Override and implement query instance equivalence properly in a subclass.
static int	floatToEdits(float minimumSimilarity, int termLen) Deprecated. pass integer edit distances instead.
int	getMaxEdits()
int	getPrefixLength() Returns the non-fuzzy prefix length.
Term	getTerm() Returns the pattern term.
protected TermsEnum	getTermsEnum(Terms terms, AttributeSource atts) Construct the enumeration to be used, expanding the pattern term.
boolean	getTranspositions() Returns true if transpositions should be treated as a primitive edit operation.
int	hashCode() Override and implement query hash code properly in a subclass.
String	toString(String field) Prints a query to a string, with field assumed to be the default field and omitted.

Methods inherited from class org.apache.lucene.search.MultiTermQuery

getField, getRewriteMethod, getTermsEnum, rewrite, setRewriteMethod

Methods inherited from class org.apache.lucene.search.Query

classHash, createWeight, sameClassAs, toString

Methods inherited from class java.lang.Object

clone, finalize, getClass, notify, notifyAll, wait, wait, wait

Field Detail

defaultMaxEdits

public static final int defaultMaxEdits

See Also:

Constant Field Values

defaultPrefixLength

public static final int defaultPrefixLength

See Also:

Constant Field Values

defaultMaxExpansions

public static final int defaultMaxExpansions

See Also:

Constant Field Values

defaultTranspositions

public static final boolean defaultTranspositions

See Also:

Constant Field Values

defaultMinSimilarity

@Deprecated
public static final float defaultMinSimilarity

Deprecated. pass integer edit distances instead.

See Also:

Constant Field Values

Constructor Detail

FuzzyQuery

public FuzzyQuery(Term term,
                  int maxEdits,
                  int prefixLength,
                  int maxExpansions,
                  boolean transpositions)

Create a new FuzzyQuery that will match terms with an edit distance of at most maxEdits to term. If a prefixLength > 0 is specified, a common prefix of that length is also required.

Parameters:

term - the term to search for

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

prefixLength - length of common (non-fuzzy) prefix

maxExpansions - the maximum number of terms to match. If this number is greater than BooleanQuery.getMaxClauseCount() when the query is rewritten, then the maxClauseCount will be used instead.

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

FuzzyQuery

public FuzzyQuery(Term term,
                  int maxEdits,
                  int prefixLength)

Calls FuzzyQuery(term, maxEdits, prefixLength, defaultMaxExpansions, defaultTranspositions).

FuzzyQuery

public FuzzyQuery(Term term,
                  int maxEdits)

Calls FuzzyQuery(term, maxEdits, defaultPrefixLength).

FuzzyQuery

public FuzzyQuery(Term term)

Calls FuzzyQuery(term, defaultMaxEdits).

Method Detail

getMaxEdits

public int getMaxEdits()

Returns:

the maximum number of edit distances allowed for this query to match.

getPrefixLength

public int getPrefixLength()

Returns the non-fuzzy prefix length. This is the number of characters at the start of a term that must be identical (not fuzzy) to the query term if the query is to match that term.

getTranspositions

public boolean getTranspositions()

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

getTermsEnum

protected TermsEnum getTermsEnum(Terms terms,
                                 AttributeSource atts)
                          throws IOException

Description copied from class: MultiTermQuery

Construct the enumeration to be used, expanding the pattern term. This method should only be called if the field exists (ie, implementations can assume the field does exist). This method should not return null (should instead return TermsEnum.EMPTY if no terms match). The TermsEnum must already be positioned to the first matching term. The given AttributeSource is passed by the MultiTermQuery.RewriteMethod to provide attributes, the rewrite method uses to inform about e.g. maximum competitive boosts. This is currently only used by TopTermsRewrite

Specified by:

getTermsEnum in class MultiTermQuery

Throws:

IOException

getTerm

public Term getTerm()

Returns the pattern term.

toString

public String toString(String field)

Description copied from class: Query

Prints a query to a string, with field assumed to be the default field and omitted.

Specified by:

toString in class Query

hashCode

public int hashCode()

Description copied from class: Query

Override and implement query hash code properly in a subclass. This is required so that QueryCache works properly.

Overrides:

hashCode in class MultiTermQuery

See Also:

Query.equals(Object)

equals

public boolean equals(Object obj)

Description copied from class: Query

Override and implement query instance equivalence properly in a subclass. This is required so that QueryCache works properly. Typically a query will be equal to another only if it's an instance of the same class and its document-filtering properties are identical that other instance. Utility methods are provided for certain repetitive code.

Overrides:

equals in class MultiTermQuery

See Also:

Query.sameClassAs(Object), Query.classHash()

floatToEdits

@Deprecated
public static int floatToEdits(float minimumSimilarity,
                                           int termLen)

Deprecated. pass integer edit distances instead.

Helper function to convert from deprecated "minimumSimilarity" fractions to raw edit distances.

Parameters:

minimumSimilarity - scaled similarity

termLen - length (in unicode codepoints) of the term.

Returns:

equivalent number of maxEdits