org.simmetrics.metrics

Class Dice<T>

java.lang.Object

org.simmetrics.metrics.Dice<T>

Type Parameters:

T - type of the token

All Implemented Interfaces:

Distance<Set<T>>, Metric<Set<T>>, SetDistance<T>, SetMetric<T>

public final class Dice<T>
extends Object
implements SetMetric<T>, SetDistance<T>

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

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

The Dice similarity coefficient is identical to SimonWhite, 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.

Similar to the overlap coefficient which divides the intersection by the size of the smaller of the two sets.

Similar to the generalized Jaccard similarity which divides the intersection by the union of two multisets.

This class is immutable and thread-safe.

See Also:

SimonWhite, OverlapCoefficient, Jaccard, Wikipedia - Sørensen–Dice coefficient

Constructor Summary

Constructors

Constructor and Description
Dice()

Method Summary

Modifier and Type	Method and Description
float	compare(Set<T> a, Set<T> b) Measures the similarity between sets a and b.
float	distance(Set<T> a, Set<T> b) Measures the distance between sets a and b.
String	toString()

Methods inherited from class java.lang.Object

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

Constructor Detail

Dice

public Dice()

Method Detail

compare

public float compare(Set<T> a,
                     Set<T> b)

Description copied from interface: SetMetric

Measures the similarity between sets 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 set1 and set2 are sets based on different equivalence relations (as HashSet, TreeSet, and the keySet of an IdentityHashMap all are).

Specified by:

compare in interface Metric<Set<T>>

Specified by:

compare in interface SetMetric<T>

Parameters:

a - set a to compare

b - set b to compare

Returns:

a value between 0 and 1 inclusive indicating similarity

distance

public float distance(Set<T> a,
                      Set<T> b)

Description copied from interface: SetDistance

Measures the distance between sets 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 sets based on different equivalence relations (as HashSet, TreeSet, and the keySet of an IdentityHashMap all are).

Specified by:

distance in interface Distance<Set<T>>

Specified by:

distance in interface SetDistance<T>

Parameters:

a - set a to compare

b - set b to compare

Returns:

a non-negative value

toString

public String toString()

Overrides:

toString in class Object