Package org.apache.lucene.search

Class 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".

    • Method Detail

      • defaultRewriteMethod

        public static MultiTermQuery.RewriteMethod defaultRewriteMethod​(int maxExpansions)
        Creates a default top-terms blended frequency scoring rewrite with the given max expansions

      • 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.

      • getAutomata

        public CompiledAutomaton getAutomata()
        Returns the compiled automata used to match terms

      • getFuzzyAutomaton

        public static CompiledAutomaton getFuzzyAutomaton​(String term,
                                                  int maxEdits,
                                                  int prefixLength,
                                                  boolean transpositions)
        Returns the CompiledAutomaton internally used by FuzzyQuery to match terms. This is a very low-level method and may no longer exist in case the implementation of fuzzy-matching changes in the future.
        Parameters:
        term - the term to search for
        maxEdits - must be >= 0 and <= LevenshteinAutomata.MAXIMUM_SUPPORTED_DISTANCE.
        prefixLength - length of common (non-fuzzy) prefix
        transpositions - true if transpositions should be treated as a primitive edit operation. If this is false, comparisons will implement the classic Levenshtein algorithm.
        Returns:
        A CompiledAutomaton that matches terms that satisfy input parameters.
        NOTE: This API is for internal purposes only and might change in incompatible ways in the next release.

      • visit

        public void visit​(QueryVisitor visitor)
        Description copied from class: Query
        Recurse through the query tree, visiting any child queries
        Specified by:
        visit in class Query
        Parameters:
        visitor - a QueryVisitor to be called by each query in the tree

      • 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

      • 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

        public static int floatToEdits​(float minimumSimilarity,
                               int termLen)
        Helper function to convert from "minimumSimilarity" fractions to raw edit distances.
        Parameters:
        minimumSimilarity - scaled similarity
        termLen - length (in unicode codepoints) of the term.
        Returns:
        equivalent number of maxEdits