    001    /*
    002     * Licensed to the Apache Software Foundation (ASF) under one or more
    003     * contributor license agreements.  See the NOTICE file distributed with
    004     * this work for additional information regarding copyright ownership.
    005     * The ASF licenses this file to You under the Apache License, Version 2.0
    006     * (the "License"); you may not use this file except in compliance with
    007     * the License.  You may obtain a copy of the License at
    008     *
    009     *      http://www.apache.org/licenses/LICENSE-2.0
    010     *
    011     * Unless required by applicable law or agreed to in writing, software
    012     * distributed under the License is distributed on an "AS IS" BASIS,
    013     * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
    014     * See the License for the specific language governing permissions and
    015     * limitations under the License.
    016     */
    017    package org.apache.commons.math3.stat.descriptive.summary;
    018
    019    import java.io.Serializable;
    020
    021    import org.apache.commons.math3.exception.MathIllegalArgumentException;
    022    import org.apache.commons.math3.exception.NullArgumentException;
    023    import org.apache.commons.math3.stat.descriptive.AbstractStorelessUnivariateStatistic;
    024    import org.apache.commons.math3.util.FastMath;
    025    import org.apache.commons.math3.util.MathUtils;
    026
    027    /**
    028     * Returns the sum of the natural logs for this collection of values.
    029     * <p>
    030     * Uses {@link org.apache.commons.math3.util.FastMath#log(double)} to compute the logs.
    031     * Therefore,
    032     * <ul>
    033     * <li>If any of values are &lt; 0, the result is <code>NaN.</code></li>
    034     * <li>If all values are non-negative and less than
    035     * <code>Double.POSITIVE_INFINITY</code>,  but at least one value is 0, the
    036     * result is <code>Double.NEGATIVE_INFINITY.</code></li>
    037     * <li>If both <code>Double.POSITIVE_INFINITY</code> and
    038     * <code>Double.NEGATIVE_INFINITY</code> are among the values, the result is
    039     * <code>NaN.</code></li>
    040     * </ul></p>
    041     * <p>
    042     * <strong>Note that this implementation is not synchronized.</strong> If
    043     * multiple threads access an instance of this class concurrently, and at least
    044     * one of the threads invokes the <code>increment()</code> or
    045     * <code>clear()</code> method, it must be synchronized externally.</p>
    046     *
    047     * @version $Id: SumOfLogs.java 1416643 2012-12-03 19:37:14Z tn $
    048     */
    049    public class SumOfLogs extends AbstractStorelessUnivariateStatistic implements Serializable {
    050
    051        /** Serializable version identifier */
    052        private static final long serialVersionUID = -370076995648386763L;
    053
    054        /**Number of values that have been added */
    055        private int n;
    056
    057        /**
    058         * The currently running value
    059         */
    060        private double value;
    061
    062        /**
    063         * Create a SumOfLogs instance
    064         */
    065        public SumOfLogs() {
    066           value = 0d;
    067           n = 0;
    068        }
    069
    070        /**
    071         * Copy constructor, creates a new {@code SumOfLogs} identical
    072         * to the {@code original}
    073         *
    074         * @param original the {@code SumOfLogs} instance to copy
    075         * @throws NullArgumentException if original is null
    076         */
    077        public SumOfLogs(SumOfLogs original) throws NullArgumentException {
    078            copy(original, this);
    079        }
    080
    081        /**
    082         * {@inheritDoc}
    083         */
    084        @Override
    085        public void increment(final double d) {
    086            value += FastMath.log(d);
    087            n++;
    088        }
    089
    090        /**
    091         * {@inheritDoc}
    092         */
    093        @Override
    094        public double getResult() {
    095            return value;
    096        }
    097
    098        /**
    099         * {@inheritDoc}
    100         */
    101        public long getN() {
    102            return n;
    103        }
    104
    105        /**
    106         * {@inheritDoc}
    107         */
    108        @Override
    109        public void clear() {
    110            value = 0d;
    111            n = 0;
    112        }
    113
    114        /**
    115         * Returns the sum of the natural logs of the entries in the specified portion of
    116         * the input array, or <code>Double.NaN</code> if the designated subarray
    117         * is empty.
    118         * <p>
    119         * Throws <code>MathIllegalArgumentException</code> if the array is null.</p>
    120         * <p>
    121         * See {@link SumOfLogs}.</p>
    122         *
    123         * @param values the input array
    124         * @param begin index of the first array element to include
    125         * @param length the number of elements to include
    126         * @return the sum of the natural logs of the values or 0 if
    127         * length = 0
    128         * @throws MathIllegalArgumentException if the array is null or the array index
    129         *  parameters are not valid
    130         */
    131        @Override
    132        public double evaluate(final double[] values, final int begin, final int length)
    133        throws MathIllegalArgumentException {
    134            double sumLog = Double.NaN;
    135            if (test(values, begin, length, true)) {
    136                sumLog = 0.0;
    137                for (int i = begin; i < begin + length; i++) {
    138                    sumLog += FastMath.log(values[i]);
    139                }
    140            }
    141            return sumLog;
    142        }
    143
    144        /**
    145         * {@inheritDoc}
    146         */
    147        @Override
    148        public SumOfLogs copy() {
    149            SumOfLogs result = new SumOfLogs();
    150            // No try-catch or advertised exception here because args are valid
    151            copy(this, result);
    152            return result;
    153        }
    154
    155        /**
    156         * Copies source to dest.
    157         * <p>Neither source nor dest can be null.</p>
    158         *
    159         * @param source SumOfLogs to copy
    160         * @param dest SumOfLogs to copy to
    161         * @throws NullArgumentException if either source or dest is null
    162         */
    163        public static void copy(SumOfLogs source, SumOfLogs dest)
    164            throws NullArgumentException {
    165            MathUtils.checkNotNull(source);
    166            MathUtils.checkNotNull(dest);
    167            dest.setData(source.getDataRef());
    168            dest.n = source.n;
    169            dest.value = source.value;
    170        }
    171    }