Class LevenshteinDetailedDistance

java.lang.Object
org.apache.commons.text.similarity.LevenshteinDetailedDistance
All Implemented Interfaces:
EditDistance<LevenshteinResults>, SimilarityScore<LevenshteinResults>

public class LevenshteinDetailedDistance extends Object implements EditDistance<LevenshteinResults>
An algorithm for measuring the difference between two character sequences.

This is the number of changes needed to change one sequence into another, where each change is a single character modification (deletion, insertion or substitution).

Since:
1.0
  • Field Details

  • Constructor Details

    • LevenshteinDetailedDistance

      public LevenshteinDetailedDistance()

      This returns the default instance that uses a version of the algorithm that does not use a threshold parameter.

      See Also:
    • LevenshteinDetailedDistance

      public LevenshteinDetailedDistance(Integer threshold)
      If the threshold is not null, distance calculations will be limited to a maximum length.

      If the threshold is null, the unlimited version of the algorithm will be used.

      Parameters:
      threshold - If this is null then distances calculations will not be limited. This may not be negative.
  • Method Details

    • apply

      public LevenshteinResults apply(CharSequence left, CharSequence right)

      Find the Levenshtein distance between two Strings.

      A higher score indicates a greater distance.

      The previous implementation of the Levenshtein distance algorithm was from http://www.merriampark.com/ld.htm

      Chas Emerick has written an implementation in Java, which avoids an OutOfMemoryError which can occur when my Java implementation is used with very large strings.
      This implementation of the Levenshtein distance algorithm is from http://www.merriampark.com/ldjava.htm

       distance.apply(null, *)             = IllegalArgumentException
       distance.apply(*, null)             = IllegalArgumentException
       distance.apply("","")               = 0
       distance.apply("","a")              = 1
       distance.apply("aaapppp", "")       = 7
       distance.apply("frog", "fog")       = 1
       distance.apply("fly", "ant")        = 3
       distance.apply("elephant", "hippo") = 7
       distance.apply("hippo", "elephant") = 7
       distance.apply("hippo", "zzzzzzzz") = 8
       distance.apply("hello", "hallo")    = 1
       
      Specified by:
      apply in interface EditDistance<LevenshteinResults>
      Specified by:
      apply in interface SimilarityScore<LevenshteinResults>
      Parameters:
      left - the first string, must not be null
      right - the second string, must not be null
      Returns:
      result distance, or -1
      Throws:
      IllegalArgumentException - if either String input null
    • getDefaultInstance

      public static LevenshteinDetailedDistance getDefaultInstance()
      Gets the default instance.
      Returns:
      The default instace
    • getThreshold

      public Integer getThreshold()
      Gets the distance threshold.
      Returns:
      The distance threshold
    • limitedCompare

      private static LevenshteinResults limitedCompare(CharSequence left, CharSequence right, int threshold)
      Find the Levenshtein distance between two CharSequences if it's less than or equal to a given threshold.

      This implementation follows from Algorithms on Strings, Trees and Sequences by Dan Gusfield and Chas Emerick's implementation of the Levenshtein distance algorithm from http://www.merriampark.com/ld.htm

       limitedCompare(null, *, *)             = IllegalArgumentException
       limitedCompare(*, null, *)             = IllegalArgumentException
       limitedCompare(*, *, -1)               = IllegalArgumentException
       limitedCompare("","", 0)               = 0
       limitedCompare("aaapppp", "", 8)       = 7
       limitedCompare("aaapppp", "", 7)       = 7
       limitedCompare("aaapppp", "", 6))      = -1
       limitedCompare("elephant", "hippo", 7) = 7
       limitedCompare("elephant", "hippo", 6) = -1
       limitedCompare("hippo", "elephant", 7) = 7
       limitedCompare("hippo", "elephant", 6) = -1
       
      Parameters:
      left - the first CharSequence, must not be null
      right - the second CharSequence, must not be null
      threshold - the target threshold, must not be negative
      Returns:
      result distance, or -1
    • unlimitedCompare

      private static LevenshteinResults unlimitedCompare(CharSequence left, CharSequence right)

      Find the Levenshtein distance between two Strings.

      A higher score indicates a greater distance.

      The previous implementation of the Levenshtein distance algorithm was from http://www.merriampark.com/ld.htm

      Chas Emerick has written an implementation in Java, which avoids an OutOfMemoryError which can occur when my Java implementation is used with very large strings.
      This implementation of the Levenshtein distance algorithm is from http://www.merriampark.com/ldjava.htm

       unlimitedCompare(null, *)             = IllegalArgumentException
       unlimitedCompare(*, null)             = IllegalArgumentException
       unlimitedCompare("","")               = 0
       unlimitedCompare("","a")              = 1
       unlimitedCompare("aaapppp", "")       = 7
       unlimitedCompare("frog", "fog")       = 1
       unlimitedCompare("fly", "ant")        = 3
       unlimitedCompare("elephant", "hippo") = 7
       unlimitedCompare("hippo", "elephant") = 7
       unlimitedCompare("hippo", "zzzzzzzz") = 8
       unlimitedCompare("hello", "hallo")    = 1
       
      Parameters:
      left - the first CharSequence, must not be null
      right - the second CharSequence, must not be null
      Returns:
      result distance, or -1
      Throws:
      IllegalArgumentException - if either CharSequence input is null
    • findDetailedResults

      private static LevenshteinResults findDetailedResults(CharSequence left, CharSequence right, int[][] matrix, boolean swapped)
      Finds count for each of the three [insert, delete, substitute] operations needed. This is based on the matrix formed based on the two character sequence.
      Parameters:
      left - character sequence which need to be converted from
      right - character sequence which need to be converted to
      matrix - two dimensional array containing
      swapped - tells whether the value for left character sequence and right character sequence were swapped to save memory
      Returns:
      result object containing the count of insert, delete and substitute and total count needed