org.simmetrics.MultisetDistance Maven / Gradle / Ivy
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* 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
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* WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
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package org.simmetrics;
import com.google.common.collect.Multiset;
import com.google.common.collect.Multisets;
/**
* Measures the unnormalized dissimilarity between two arbitrary multisets
* containing elements of the same type. The measurement results in a value
* between 0 and 1 inclusive. A value of zero indicates that the lists are
* dissimilar, a value of 1 indicates they are similar.
*
* The elements in the multisets have to implement {@link Object#hashCode()} and
* {@link Object#equals(Object)}.
*
* The elements in the multisets may not be null if metric does not support null
* values.
*
* 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 multisets. Multisets
* should be treated as if wrapped by
* {@link Multisets#unmodifiableMultiset(Multiset)}.
*
* @see Wikipedia -
* Metric
*
* @param
* the type of elements contained in the lists
*/
public interface MultisetDistance extends Distance> {
/**
* Measures the distance between multisets 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 based on different
* equivalence relations (as {@code HashMultiset} and {@code TreeMultiset}
* are).
*
* @param a
* list a to compare
* @param b
* list b to compare
* @return a non-negative value
* @throws NullPointerException
* when either a or b is null
*/
@Override
public float distance(Multiset a, Multiset b);
}