org.simmetrics.metrics

Class SimonWhite<T>

java.lang.Object

org.simmetrics.metrics.SimonWhite<T>

Type Parameters:

T - type of the token

All Implemented Interfaces:

Distance<com.google.common.collect.Multiset<T>>, Metric<com.google.common.collect.Multiset<T>>, MultisetDistance<T>, MultisetMetric<T>

public final class SimonWhite<T>
extends Object
implements MultisetMetric<T>, MultisetDistance<T>

Calculates the Dice similarity coefficient and distance over two multisets. Also known as quantitative version of the Dice similarity coefficient. The similarity is defined as twice the shared information (intersection) divided by the sum of cardinalities.

similarity(a,b) = 2 * ∣a ∩ b∣ / (∣a∣ + ∣b∣)
distance(a,b) = 1 - similarity(a,b)

Implementation based on the ideas as outlined in How to Strike a Match by Simon White. To create the described metric use:

 import static org.simmetrics.StringMetricBuilder.with;
  
  ...
  
 with(new SimonWhite<String>())
   .tokenize(Tokenizers.qGram(2))
   .build();
 
 

The Dice similarity coefficient is identical to Simon White, but unlike Simon White the occurrence (cardinality) of an entry is not taken into account. E.g. [hello, world] and [hello, world, hello, world] would be identical when compared with Dice but are dissimilar when Simon White is used.

This class is immutable and thread-safe.

See Also:

Dice, Wikipedia - Sørensen–Dice coefficient

Constructor Summary

Constructors

Constructor and Description
SimonWhite()

Method Summary

Modifier and Type	Method and Description
float	compare(com.google.common.collect.Multiset<T> a, com.google.common.collect.Multiset<T> b) Measures the similarity between multisets a and b.
float	distance(com.google.common.collect.Multiset<T> a, com.google.common.collect.Multiset<T> b) Measures the distance between multisets a and b.
String	toString()

Methods inherited from class java.lang.Object

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

Constructor Detail

SimonWhite

public SimonWhite()

Method Detail

compare

public float compare(com.google.common.collect.Multiset<T> a,
                     com.google.common.collect.Multiset<T> b)

Description copied from interface: MultisetMetric

Measures the similarity between multisets a and b. The measurement results in a value between 0 and 1 inclusive. A value of zero indicates that the sets are dissimilar, a value of 1 indicates they are similar.

Results are undefined if a and b are based on different equivalence relations (as HashMultiset and TreeMultiset are).

Specified by:

compare in interface Metric<com.google.common.collect.Multiset<T>>

Specified by:

compare in interface MultisetMetric<T>

Parameters:

a - multisets a to compare

b - multisets b to compare

Returns:

a value between 0 and 1 inclusive indicating similarity

distance

public float distance(com.google.common.collect.Multiset<T> a,
                      com.google.common.collect.Multiset<T> b)

Description copied from interface: MultisetDistance

Measures the distance between multisets a and b. The measurement results in a non-negative value. A value of 0.0 indicates that a and b are similar.

Results are undefined if a and b are based on different equivalence relations (as HashMultiset and TreeMultiset are).

Specified by:

distance in interface Distance<com.google.common.collect.Multiset<T>>

Specified by:

distance in interface MultisetDistance<T>

Parameters:

a - list a to compare

b - list b to compare

Returns:

a non-negative value

toString

public String toString()

Overrides:

toString in class Object