/*
 * 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.math3.stat.descriptive.summary;

import java.io.Serializable;

import org.apache.commons.math3.exception.MathIllegalArgumentException;
import org.apache.commons.math3.exception.NullArgumentException;
import org.apache.commons.math3.stat.descriptive.AbstractStorelessUnivariateStatistic;
import org.apache.commons.math3.stat.descriptive.WeightedEvaluation;
import org.apache.commons.math3.util.FastMath;
import org.apache.commons.math3.util.MathUtils;

Returns the product of the available values.

If there are no values in the dataset, then 1 is returned.
 If any of the values are
NaN, then NaN is returned.

Note that this implementation is not synchronized. If
multiple threads access an instance of this class concurrently, and at least
one of the threads invokes the increment() or
clear() method, it must be synchronized externally.
/**
 * 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 Serializable, WeightedEvaluation {

    
Serializable version identifier /** Serializable version identifier */
    private static final long serialVersionUID = 2824226005990582538L;

    
The number of values that have been added /**The number of values that have been added */
    private long n;

    
The current Running Product.
/**
     * The current Running Product.
     */
    private double value;

    
Create a Product instance
/**
     * Create a Product instance
     */
    public Product() {
        n = 0;
        value = 1;
    }

    
Copy constructor, creates a new Product identical to the original 
Params:
original – the Product instance to copy
Throws:
NullArgumentException –  if original is null/**
     * 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}
/**
     * {@inheritDoc}
     */
    @Override
    public void increment(final double d) {
        value *= d;
        n++;
    }

    
{@inheritDoc}
/**
     * {@inheritDoc}
     */
    @Override
    public double getResult() {
        return value;
    }

    
{@inheritDoc}
/**
     * {@inheritDoc}
     */
    public long getN() {
        return n;
    }

    
{@inheritDoc}
/**
     * {@inheritDoc}
     */
    @Override
    public void clear() {
        value = 1;
        n = 0;
    }

    
Returns the product of the entries in the specified portion of
the input array, or Double.NaN if the designated subarray
is empty.

Throws MathIllegalArgumentException if the array is null.
Params:
values – the input array
begin – index of the first array element to include
length – the number of elements to include
Throws:
MathIllegalArgumentException – if the array is null or the array index
 parameters are not valid
Returns:
the product of the values or 1 if length = 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 (test(values, begin, length, true)) {
            product = 1.0;
            for (int i = begin; i < begin + length; i++) {
                product *= values[i];
            }
        }
        return product;
    }

    
Returns the weighted product of the entries in the specified portion of
the input array, or Double.NaN if the designated subarray
is empty.
Throws MathIllegalArgumentException if any of the following are true:
the values array is null
    
the weights array is null
    
the weights array does not have the same length as the values array
    
the weights array contains one or more infinite values
    
the weights array contains one or more NaN values
    
the weights array contains negative values
    
the start and length arguments do not determine a valid array

Uses the formula, 
   weighted product = ∏values[i]weights[i]

that is, the weights are applied as exponents when computing the weighted product.

Params:
values – the input array
weights – the weights array
begin – index of the first array element to include
length – the number of elements to include
Throws:
MathIllegalArgumentException – if the parameters are not valid
Returns:
the product of the values or 1 if length = 0
Since:
2.1/**
     * <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>
     *
     * <p>Uses the formula, <pre>
     *    weighted product = &prod;values[i]<sup>weights[i]</sup>
     * </pre>
     * that is, the weights are applied as exponents when computing the weighted product.</p>
     *
     * @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
     */
    public double evaluate(final double[] values, final double[] weights,
        final int begin, final int length) throws MathIllegalArgumentException {
        double product = Double.NaN;
        if (test(values, weights, begin, length, true)) {
            product = 1.0;
            for (int i = begin; i < begin + length; i++) {
                product *= FastMath.pow(values[i], weights[i]);
            }
        }
        return product;
    }

    
Returns the weighted product of the entries in the input array.
Throws MathIllegalArgumentException if any of the following are true:
the values array is null
    
the weights array is null
    
the weights array does not have the same length as the values array
    
the weights array contains one or more infinite values
    
the weights array contains one or more NaN values
    
the weights array contains negative values

Uses the formula, 
   weighted product = ∏values[i]weights[i]

that is, the weights are applied as exponents when computing the weighted product.

Params:
values – the input array
weights – the weights array
Throws:
MathIllegalArgumentException – if the parameters are not valid
Returns:
the product of the values or Double.NaN if length = 0
Since:
2.1/**
     * <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>
     *
     * <p>Uses the formula, <pre>
     *    weighted product = &prod;values[i]<sup>weights[i]</sup>
     * </pre>
     * that is, the weights are applied as exponents when computing the weighted product.</p>
     *
     * @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
     */
    public double evaluate(final double[] values, final double[] weights)
    throws MathIllegalArgumentException {
        return evaluate(values, weights, 0, values.length);
    }


    
{@inheritDoc}
/**
     * {@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.
Neither source nor dest can be null.
Params:
source – Product to copy
dest – Product to copy to
Throws:
NullArgumentException – if either source or dest is null/**
     * 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 {
        MathUtils.checkNotNull(source);
        MathUtils.checkNotNull(dest);
        dest.setData(source.getDataRef());
        dest.n = source.n;
        dest.value = source.value;
    }

}