org.simmetrics.SetDistance Maven / Gradle / Ivy
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* #%L
* Simmetrics Core
* %%
* Copyright (C) 2014 - 2016 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,
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* See the License for the specific language governing permissions and
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* #L%
*/
package org.simmetrics;
import java.util.Collections;
import java.util.Set;
/**
* Measures the unnormalized dissimilarity between two arbitrary sets containing
* elements of the same type. The measurement results in a non-negative value. A
* value of zero indicates that the objects are similar.
*
* The elements in the sets have to implement {@link Object#hashCode()} and
* {@link Object#equals(Object)}.
*
* The distance measure should be consistent with equals such that
* {@code a.equals(b) => distance(a,b) == 0.0}.
*
* The distance measure should be reflexive such that
* {@code distance(a,a) == 0.0}.
*
* The distance measure should be symmetric such that
* {@code distance(a,b) == distance(b,a)}.
*
* Implementations may not modify the contents of the sets. List should be
* treated as if wrapped by {@link Collections#unmodifiableSet(Set)}.
*
* @see Wikipedia -
* Metric
*
* @param
* the type of elements contained in the lists
*/
public interface SetDistance extends Distance> {
/**
* Measures the distance between sets a and b. The measurement results in a
* non-negative value. A value of {@code 0.0} indicates that {@code a} and
* {@code b} are similar.
*
* Results are undefined if {@code a} and {@code b} 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 non-negative value
* @throws NullPointerException
* when either a or b is null
*/
@Override
public float distance(Set a, Set b);
}