org.apache.commons.text.similarity

Class LevenshteinDistance

java.lang.Object

org.apache.commons.text.similarity.LevenshteinDistance

All Implemented Interfaces:

EditDistance<Integer>, SimilarityScore<Integer>

public class LevenshteinDistance
extends Object
implements EditDistance<Integer>

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).

This code has been adapted from Apache Commons Lang 3.3.

Since:

1.0

Constructor Summary

Constructors

Constructor and Description
LevenshteinDistance() This returns the default instance that uses a version of the algorithm that does not use a threshold parameter.
LevenshteinDistance(Integer threshold) If the threshold is not null, distance calculations will be limited to a maximum length.

Method Summary

Modifier and Type	Method and Description
Integer	apply(CharSequence left, CharSequence right) Find the Levenshtein distance between two Strings.
static LevenshteinDistance	getDefaultInstance() Gets the default instance.
Integer	getThreshold() Gets the distance threshold.

Methods inherited from class java.lang.Object

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

Constructor Detail

LevenshteinDistance

public LevenshteinDistance()

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

See Also:

getDefaultInstance()

LevenshteinDistance

public LevenshteinDistance(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 Detail

apply

public Integer 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<Integer>

Specified by:

apply in interface SimilarityScore<Integer>

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 LevenshteinDistance getDefaultInstance()

Gets the default instance.

Returns:

the default instace

getThreshold

public Integer getThreshold()

Gets the distance threshold.

Returns:

the distance threshold