Product.java
/*
* Licensed to the Apache Software Foundation (ASF) under one or more
* contributor license agreements. See the NOTICE file distributed with
* this work for additional information regarding copyright ownership.
* The ASF licenses this file to You 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.
*/
package org.apache.commons.math4.legacy.stat.descriptive.summary;
import org.apache.commons.math4.legacy.exception.MathIllegalArgumentException;
import org.apache.commons.math4.legacy.exception.NullArgumentException;
import org.apache.commons.math4.legacy.stat.descriptive.AbstractStorelessUnivariateStatistic;
import org.apache.commons.math4.legacy.stat.descriptive.WeightedEvaluation;
import org.apache.commons.math4.core.jdkmath.JdkMath;
import org.apache.commons.math4.legacy.core.MathArrays;
/**
* Returns the product of the available values.
* <p>
* If there are no values in the dataset, then 1 is returned.
* If any of the values are
* <code>NaN</code>, then <code>NaN</code> is returned.</p>
* <p>
* <strong>Note that this implementation is not synchronized.</strong> If
* multiple threads access an instance of this class concurrently, and at least
* one of the threads invokes the <code>increment()</code> or
* <code>clear()</code> method, it must be synchronized externally.</p>
*/
public class Product extends AbstractStorelessUnivariateStatistic implements WeightedEvaluation {
/**The number of values that have been added. */
private long n;
/**
* The current Running Product.
*/
private double value;
/**
* Create a Product instance.
*/
public Product() {
n = 0;
value = 1;
}
/**
* Copy constructor, creates a new {@code Product} identical
* to the {@code original}.
*
* @param original the {@code Product} instance to copy
* @throws NullArgumentException if original is null
*/
public Product(Product original) throws NullArgumentException {
copy(original, this);
}
/**
* {@inheritDoc}
*/
@Override
public void increment(final double d) {
value *= d;
n++;
}
/**
* {@inheritDoc}
*/
@Override
public double getResult() {
return value;
}
/**
* {@inheritDoc}
*/
@Override
public long getN() {
return n;
}
/**
* {@inheritDoc}
*/
@Override
public void clear() {
value = 1;
n = 0;
}
/**
* Returns the product of the entries in the specified portion of
* the input array, or <code>Double.NaN</code> if the designated subarray
* is empty.
* <p>
* Throws <code>MathIllegalArgumentException</code> if the array is null.</p>
*
* @param values the input array
* @param begin index of the first array element to include
* @param length the number of elements to include
* @return the product of the values or 1 if length = 0
* @throws MathIllegalArgumentException if the array is null or the array index
* parameters are not valid
*/
@Override
public double evaluate(final double[] values, final int begin, final int length)
throws MathIllegalArgumentException {
double product = Double.NaN;
if (MathArrays.verifyValues(values, begin, length, true)) {
product = 1.0;
for (int i = begin; i < begin + length; i++) {
product *= values[i];
}
}
return product;
}
/**
* <p>Returns the weighted product of the entries in the specified portion of
* the input array, or <code>Double.NaN</code> if the designated subarray
* is empty.</p>
*
* <p>Throws <code>MathIllegalArgumentException</code> if any of the following are true:
* <ul><li>the values array is null</li>
* <li>the weights array is null</li>
* <li>the weights array does not have the same length as the values array</li>
* <li>the weights array contains one or more infinite values</li>
* <li>the weights array contains one or more NaN values</li>
* <li>the weights array contains negative values</li>
* <li>the start and length arguments do not determine a valid array</li>
* </ul>
*
* <p>Uses the formula, <div style="white-space: pre"><code>
* weighted product = ∏values[i]<sup>weights[i]</sup>
* </code></div>
* that is, the weights are applied as exponents when computing the weighted product.
*
* @param values the input array
* @param weights the weights array
* @param begin index of the first array element to include
* @param length the number of elements to include
* @return the product of the values or 1 if length = 0
* @throws MathIllegalArgumentException if the parameters are not valid
* @since 2.1
*/
@Override
public double evaluate(final double[] values, final double[] weights,
final int begin, final int length) throws MathIllegalArgumentException {
double product = Double.NaN;
if (MathArrays.verifyValues(values, weights, begin, length, true)) {
product = 1.0;
for (int i = begin; i < begin + length; i++) {
product *= JdkMath.pow(values[i], weights[i]);
}
}
return product;
}
/**
* <p>Returns the weighted product of the entries in the input array.</p>
*
* <p>Throws <code>MathIllegalArgumentException</code> if any of the following are true:
* <ul><li>the values array is null</li>
* <li>the weights array is null</li>
* <li>the weights array does not have the same length as the values array</li>
* <li>the weights array contains one or more infinite values</li>
* <li>the weights array contains one or more NaN values</li>
* <li>the weights array contains negative values</li>
* </ul>
*
* <p>Uses the formula,
* <div style="white-space: pre"><code>
* weighted product = ∏values[i]<sup>weights[i]</sup>
* </code></div>
* that is, the weights are applied as exponents when computing the weighted product.
*
* @param values the input array
* @param weights the weights array
* @return the product of the values or Double.NaN if length = 0
* @throws MathIllegalArgumentException if the parameters are not valid
* @since 2.1
*/
@Override
public double evaluate(final double[] values, final double[] weights) throws MathIllegalArgumentException {
return evaluate(values, weights, 0, values.length);
}
/**
* {@inheritDoc}
*/
@Override
public Product copy() {
Product result = new Product();
// No try-catch or advertised exception because args are valid
copy(this, result);
return result;
}
/**
* Copies source to dest.
* <p>Neither source nor dest can be null.</p>
*
* @param source Product to copy
* @param dest Product to copy to
* @throws NullArgumentException if either source or dest is null
*/
public static void copy(Product source, Product dest)
throws NullArgumentException {
NullArgumentException.check(source);
NullArgumentException.check(dest);
dest.n = source.n;
dest.value = source.value;
}
}