org.simmetrics.metrics.BlockDistance.java Source code

Introduction

Here is the source code for org.simmetrics.metrics.BlockDistance.java

Source

/*
 * #%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,
 * 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.metrics;

import static java.lang.Math.abs;
import static org.simmetrics.metrics.Math.union;

import org.simmetrics.MultisetDistance;
import org.simmetrics.MultisetMetric;

import com.google.common.collect.Multiset;

/**
 * Calculates the block distance and similarity over two multisets. Also known
 * as L1 Distance or City block distance.
 * <p>
 * <code>
 * similarity(a,b) = 1 - distance(a,b) / (a + b)
 * <br>
 * distance(a,b) = a - b?
 * </code>
 * <p>
 * This class is immutable and thread-safe.
 * 
 * @see <a href="http://en.wikipedia.org/wiki/Taxicab_geometry">Wikipedia -
 *      Taxicab geometry</a>
 * @param <T>
 *            type of token
 */
public final class BlockDistance<T> implements MultisetMetric<T>, MultisetDistance<T> {

    @Override
    public float compare(Multiset<T> a, Multiset<T> b) {

        if (a.isEmpty() && b.isEmpty()) {
            return 1.0f;
        }

        if (a.isEmpty() || b.isEmpty()) {
            return 0.0f;
        }

        return 1.0f - distance(a, b) / (a.size() + b.size());
    }

    @Override
    public float distance(Multiset<T> a, Multiset<T> b) {

        float distance = 0;

        for (T token : union(a, b).elementSet()) {
            float frequencyInA = a.count(token);
            float frequencyInB = b.count(token);

            distance += abs(frequencyInA - frequencyInB);
        }
        return distance;
    }

    @Override
    public String toString() {
        return "BlockDistance";
    }

}