org.simmetrics.SetMetric Maven / Gradle / Ivy
/*
* #%L
* Simmetrics Core
* %%
* Copyright (C) 2014 - 2015 Simmetrics Authors
* %%
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
* #L%
*/
package org.simmetrics;
import java.util.Collections;
import java.util.Set;
/**
* Measures the similarity between two arbitrary sets containing elements of the
* same type. 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.
*
*
* The elements in the set have to implement {@link Object#hashCode()} and
* {@link Object#equals(Object)}.
*
* The elements in the sets may not be null if metric does not support null
* values.
*
* The similarity measure should be consistent with equals such that
* {@code a.equals(b) => compare(a,b) == 1.0}.
*
* The similarity measure should be reflexive such that
* {@code compare(a,a) == 1.0}.
*
* The similarity measure should be symmetric such that
* {@code compare(a,b) == compare(b,a)}.
*
* Implementations may not modify the contents of the set. Sets should be
* treated as if wrapped by {@link Collections#unmodifiableSet(Set)}.
*
* @param
* the type of elements contained in the sets
*
*/
public interface SetMetric extends Metric> {
/**
* 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 {@code set1} and {@code set2} are sets based on
* different equivalence relations (as {@code HashSet}, {@code TreeSet}, and
* the keySet of an {@code IdentityHashMap} all are).
*
* @param a
* set a to compare
* @param b
* set b to compare
* @return a value between 0 and 1 inclusive indicating similarity
* @throws NullPointerException
* when either a or b is null
*/
@Override
public float compare(Set a, Set b);
}