Package org.apache.commons.text.similarity

Class LevenshteinDistance

java.lang.Object

org.apache.commons.text.similarity.LevenshteinDistance

All Implemented Interfaces:

java.util.function.BiFunction<java.lang.CharSequence,java.lang.CharSequence,java.lang.Integer>, EditDistance<java.lang.Integer>, ObjectSimilarityScore<java.lang.CharSequence,java.lang.Integer>, SimilarityScore<java.lang.Integer>

public class LevenshteinDistance
extends java.lang.Object
implements EditDistance<java.lang.Integer>

An algorithm for measuring the difference between two character sequences using the Levenshtein Distance.

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

See Also:

Levenshtein Distance on Wikipedia, Levenshtein Distance on NIST

Constructor Summary

Constructors

Constructor	Description
LevenshteinDistance()	Deprecated. Use getDefaultInstance().
LevenshteinDistance(java.lang.Integer threshold)	Constructs a new instance.

Method Summary

Modifier and Type	Method	Description
java.lang.Integer	apply(java.lang.CharSequence left, java.lang.CharSequence right)	Computes the Levenshtein distance between two Strings.
<E> java.lang.Integer	apply(SimilarityInput<E> left, SimilarityInput<E> right)	Computes the Levenshtein distance between two inputs.
static LevenshteinDistance	getDefaultInstance()	Gets the default instance.
java.lang.Integer	getThreshold()	Gets the distance threshold.

Methods inherited from class java.lang.Object

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

Methods inherited from interface java.util.function.BiFunction

andThen

Constructor Detail

LevenshteinDistance

@Deprecated
public LevenshteinDistance()

Deprecated.

Use getDefaultInstance().

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

See Also:

getDefaultInstance()

LevenshteinDistance

public LevenshteinDistance(java.lang.Integer threshold)

Constructs a new instance. 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

getDefaultInstance

public static LevenshteinDistance getDefaultInstance()

Gets the default instance.

Returns:

The default instance.

apply

public java.lang.Integer apply(java.lang.CharSequence left,
                               java.lang.CharSequence right)

Computes 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, *)             = Throws IllegalArgumentException
 distance.apply(*, null)             = Throws 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 java.util.function.BiFunction<java.lang.CharSequence,java.lang.CharSequence,java.lang.Integer>

Specified by:

apply in interface ObjectSimilarityScore<java.lang.CharSequence,java.lang.Integer>

Specified by:

apply in interface SimilarityScore<java.lang.Integer>

Parameters:

left - the first input, must not be null.

right - the second input, must not be null.

Returns:

result distance, or -1.

Throws:

java.lang.IllegalArgumentException - if either String input null.

apply

public <E> java.lang.Integer apply(SimilarityInput<E> left,
                                   SimilarityInput<E> right)

Computes the Levenshtein distance between two inputs.

A higher score indicates a greater distance.

 distance.apply(null, *)             = Throws IllegalArgumentException
 distance.apply(*, null)             = Throws 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
 

Type Parameters:

E - The type of similarity score unit.

Parameters:

left - the first input, must not be null.

right - the second input, must not be null.

Returns:

result distance, or -1.

Throws:

java.lang.IllegalArgumentException - if either String input null.

Since:

1.13.0

getThreshold

public java.lang.Integer getThreshold()

Gets the distance threshold.

Returns:

The distance threshold.