SumOfLogs.java

  1. /*
  2.  * Licensed to the Apache Software Foundation (ASF) under one or more
  3.  * contributor license agreements.  See the NOTICE file distributed with
  4.  * this work for additional information regarding copyright ownership.
  5.  * The ASF licenses this file to You under the Apache License, Version 2.0
  6.  * (the "License"); you may not use this file except in compliance with
  7.  * the License.  You may obtain a copy of the License at
  8.  *
  9.  *      http://www.apache.org/licenses/LICENSE-2.0
  10.  *
  11.  * Unless required by applicable law or agreed to in writing, software
  12.  * distributed under the License is distributed on an "AS IS" BASIS,
  13.  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  14.  * See the License for the specific language governing permissions and
  15.  * limitations under the License.
  16.  */
  17. package org.apache.commons.statistics.descriptive;

  19. /**
  20.  * Returns the sum of the {@link Math#log(double) natural logarithm} of available values.
  21.  *
  22.  * <ul>
  23.  *   <li>The result is zero if no values are added.
  24.  *   <li>The result is {@code NaN} if any of the values is {@code NaN}.
  25.  *   <li>The result is {@code NaN} if any of the values is negative.
  26.  * </ul>
  27.  *
  28.  * <p>The sum follows the IEEE754 result for summing infinite values:
  29.  *
  30.  * <ul>
  31.  *   <li>The result is {@code +infinity} if all values are in the range {@code (0, +infinity]}
  32.  *       and at least one value is {@code +infinity}.
  33.  *   <li>The result is {@code -infinity} if all values are in the range {@code [0, +infinity)}
  34.  *       and at least one value is zero.
  35.  *   <li>The result is {@code NaN} if all values are in the range {@code [0, +infinity]}
  36.  *       and at least one value is zero, and one value is {@code +infinity}.
  37.  * </ul>
  38.  *
  39.  * <p>This class is designed to work with (though does not require)
  40.  * {@linkplain java.util.stream streams}.
  41.  *
  42.  * <p><strong>This instance is not thread safe.</strong>
  43.  * If multiple threads access an instance of this class concurrently,
  44.  * and at least one of the threads invokes the {@link java.util.function.DoubleConsumer#accept(double) accept} or
  45.  * {@link StatisticAccumulator#combine(StatisticResult) combine} method, it must be synchronized externally.
  46.  *
  47.  * <p>However, it is safe to use {@link java.util.function.DoubleConsumer#accept(double) accept}
  48.  * and {@link StatisticAccumulator#combine(StatisticResult) combine}
  49.  * as {@code accumulator} and {@code combiner} functions of
  50.  * {@link java.util.stream.Collector Collector} on a parallel stream,
  51.  * because the parallel instance of {@link java.util.stream.Stream#collect Stream.collect()}
  52.  * provides the necessary partitioning, isolation, and merging of results for
  53.  * safe and efficient parallel execution.
  54.  *
  55.  * @see org.apache.commons.numbers.core.Sum
  56.  * @see Math#log(double)
  57.  * @since 1.1
  58.  */
  59. public final class SumOfLogs implements DoubleStatistic, StatisticAccumulator<SumOfLogs> {

  61.     /** {@link org.apache.commons.numbers.core.Sum Sum} used to compute the sum. */
  62.     private final org.apache.commons.numbers.core.Sum delegate =
  63.             org.apache.commons.numbers.core.Sum.create();

  65.     /**
  66.      * Create an instance.
  67.      */
  68.     private SumOfLogs() {
  69.         // No-op
  70.     }

  72.     /**
  73.      * Creates an instance.
  74.      *
  75.      * <p>The initial result is zero.
  76.      *
  77.      * @return {@code SumOfLogs} instance.
  78.      */
  79.     public static SumOfLogs create() {
  80.         return new SumOfLogs();
  81.     }

  83.     /**
  84.      * Returns an instance populated using the input {@code values}.
  85.      *
  86.      * <p>The result is {@code NaN} if any of the values is {@code NaN}
  87.      * or negative; or the sum at any point is a {@code NaN}.
  88.      *
  89.      * <p>When the input is an empty array, the result is zero.
  90.      *
  91.      * @param values Values.
  92.      * @return {@code SumOfLogs} instance.
  93.      */
  94.     public static SumOfLogs of(double... values) {
  95.         return Statistics.add(new SumOfLogs(), values);
  96.     }

  98.     /**
  99.      * Returns an instance populated using the specified range of {@code values}.
  100.      *
  101.      * <p>The result is {@code NaN} if any of the values is {@code NaN}
  102.      * or negative; or the sum at any point is a {@code NaN}.
  103.      *
  104.      * <p>When the range is empty, the result is zero.
  105.      *
  106.      * @param values Values.
  107.      * @param from Inclusive start of the range.
  108.      * @param to Exclusive end of the range.
  109.      * @return {@code SumOfLogs} instance.
  110.      * @throws IndexOutOfBoundsException if the sub-range is out of bounds
  111.      * @since 1.2
  112.      */
  113.     public static SumOfLogs ofRange(double[] values, int from, int to) {
  114.         Statistics.checkFromToIndex(from, to, values.length);
  115.         return createFromRange(values, from, to);
  116.     }

  118.     /**
  119.      * Create an instance using the specified range of {@code values}.
  120.      *
  121.      * <p>Warning: No range checks are performed.
  122.      *
  123.      * @param values Values.
  124.      * @param from Inclusive start of the range.
  125.      * @param to Exclusive end of the range.
  126.      * @return {@code SumOfLogs} instance.
  127.      */
  128.     static SumOfLogs createFromRange(double[] values, int from, int to) {
  129.         return Statistics.add(new SumOfLogs(), values, from, to);
  130.     }

  132.     /**
  133.      * Returns an instance populated using the input {@code values}.
  134.      *
  135.      * <p>The result is {@code NaN} if any of the values is negative.
  136.      *
  137.      * <p>When the input is an empty array, the result is zero.
  138.      *
  139.      * @param values Values.
  140.      * @return {@code SumOfLogs} instance.
  141.      */
  142.     public static SumOfLogs of(int... values) {
  143.         return Statistics.add(new SumOfLogs(), values);
  144.     }

  146.     /**
  147.      * Returns an instance populated using the specified range of {@code values}.
  148.      *
  149.      * <p>The result is {@code NaN} if any of the values is negative.
  150.      *
  151.      * <p>When the range is empty, the result is zero.
  152.      *
  153.      * @param values Values.
  154.      * @param from Inclusive start of the range.
  155.      * @param to Exclusive end of the range.
  156.      * @return {@code SumOfLogs} instance.
  157.      * @throws IndexOutOfBoundsException if the sub-range is out of bounds
  158.      * @since 1.2
  159.      */
  160.     public static SumOfLogs ofRange(int[] values, int from, int to) {
  161.         Statistics.checkFromToIndex(from, to, values.length);
  162.         return createFromRange(values, from, to);
  163.     }

  165.     /**
  166.      * Create an instance using the specified range of {@code values}.
  167.      *
  168.      * <p>Warning: No range checks are performed.
  169.      *
  170.      * @param values Values.
  171.      * @param from Inclusive start of the range.
  172.      * @param to Exclusive end of the range.
  173.      * @return {@code SumOfLogs} instance.
  174.      */
  175.     static SumOfLogs createFromRange(int[] values, int from, int to) {
  176.         return Statistics.add(new SumOfLogs(), values, from, to);
  177.     }

  179.     /**
  180.      * Returns an instance populated using the input {@code values}.
  181.      *
  182.      * <p>The result is {@code NaN} if any of the values is negative.
  183.      *
  184.      * <p>When the input is an empty array, the result is zero.
  185.      *
  186.      * @param values Values.
  187.      * @return {@code SumOfLogs} instance.
  188.      */
  189.     public static SumOfLogs of(long... values) {
  190.         return Statistics.add(new SumOfLogs(), values);
  191.     }

  193.     /**
  194.      * Returns an instance populated using the specified range of {@code values}.
  195.      *
  196.      * <p>The result is {@code NaN} if any of the values is negative.
  197.      *
  198.      * <p>When the range is empty, the result is zero.
  199.      *
  200.      * @param values Values.
  201.      * @param from Inclusive start of the range.
  202.      * @param to Exclusive end of the range.
  203.      * @return {@code SumOfLogs} instance.
  204.      * @throws IndexOutOfBoundsException if the sub-range is out of bounds
  205.      * @since 1.2
  206.      */
  207.     public static SumOfLogs ofRange(long[] values, int from, int to) {
  208.         Statistics.checkFromToIndex(from, to, values.length);
  209.         return createFromRange(values, from, to);
  210.     }

  212.     /**
  213.      * Create an instance using the specified range of {@code values}.
  214.      *
  215.      * <p>Warning: No range checks are performed.
  216.      *
  217.      * @param values Values.
  218.      * @param from Inclusive start of the range.
  219.      * @param to Exclusive end of the range.
  220.      * @return {@code SumOfLogs} instance.
  221.      */
  222.     static SumOfLogs createFromRange(long[] values, int from, int to) {
  223.         return Statistics.add(new SumOfLogs(), values, from, to);
  224.     }

  226.     /**
  227.      * Updates the state of the statistic to reflect the addition of {@code value}.
  228.      *
  229.      * @param value Value.
  230.      */
  231.     @Override
  232.     public void accept(double value) {
  233.         delegate.accept(Math.log(value));
  234.     }

  236.     /**
  237.      * Gets the sum of all input values.
  238.      *
  239.      * <p>When no values have been added, the result is zero.
  240.      *
  241.      * @return sum of all values.
  242.      */
  243.     @Override
  244.     public double getAsDouble() {
  245.         return delegate.getAsDouble();
  246.     }

  248.     @Override
  249.     public SumOfLogs combine(SumOfLogs other) {
  250.         delegate.add(other.delegate);
  251.         return this;
  252.     }
  253. }
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