319 lines
12 KiB
Java
319 lines
12 KiB
Java
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/*
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* Copyright (c) 2012, 2019, Oracle and/or its affiliates. All rights reserved.
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* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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*
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* This code is free software; you can redistribute it and/or modify it
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* under the terms of the GNU General Public License version 2 only, as
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* published by the Free Software Foundation. Oracle designates this
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* particular file as subject to the "Classpath" exception as provided
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* by Oracle in the LICENSE file that accompanied this code.
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*
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* This code is distributed in the hope that it will be useful, but WITHOUT
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* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
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* FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
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* version 2 for more details (a copy is included in the LICENSE file that
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* accompanied this code).
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*
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* You should have received a copy of the GNU General Public License version
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* 2 along with this work; if not, write to the Free Software Foundation,
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* Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
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*
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* Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
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* or visit www.oracle.com if you need additional information or have any
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* questions.
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*/
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package java.util;
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import java.util.function.DoubleConsumer;
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import java.util.stream.Collector;
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import java.util.stream.DoubleStream;
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/**
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* A state object for collecting statistics such as count, min, max, sum, and
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* average.
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*
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* <p>This class is designed to work with (though does not require)
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* {@linkplain java.util.stream streams}. For example, you can compute
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* summary statistics on a stream of doubles with:
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* <pre> {@code
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* DoubleSummaryStatistics stats = doubleStream.collect(DoubleSummaryStatistics::new,
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* DoubleSummaryStatistics::accept,
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* DoubleSummaryStatistics::combine);
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* }</pre>
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*
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* <p>{@code DoubleSummaryStatistics} can be used as a
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* {@linkplain java.util.stream.Stream#collect(Collector) reduction}
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* target for a {@linkplain java.util.stream.Stream stream}. For example:
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*
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* <pre> {@code
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* DoubleSummaryStatistics stats = people.stream()
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* .collect(Collectors.summarizingDouble(Person::getWeight));
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*}</pre>
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*
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* This computes, in a single pass, the count of people, as well as the minimum,
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* maximum, sum, and average of their weights.
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*
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* @implNote This implementation is not thread safe. However, it is safe to use
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* {@link java.util.stream.Collectors#summarizingDouble(java.util.function.ToDoubleFunction)
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* Collectors.summarizingDouble()} on a parallel stream, because the parallel
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* implementation of {@link java.util.stream.Stream#collect Stream.collect()}
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* provides the necessary partitioning, isolation, and merging of results for
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* safe and efficient parallel execution.
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*
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* <p>This implementation does not check for overflow of the count.
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* @since 1.8
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*/
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public class DoubleSummaryStatistics implements DoubleConsumer {
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private long count;
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private double sum;
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private double sumCompensation; // Low order bits of sum
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private double simpleSum; // Used to compute right sum for non-finite inputs
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private double min = Double.POSITIVE_INFINITY;
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private double max = Double.NEGATIVE_INFINITY;
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/**
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* Constructs an empty instance with zero count, zero sum,
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* {@code Double.POSITIVE_INFINITY} min, {@code Double.NEGATIVE_INFINITY}
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* max and zero average.
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*/
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public DoubleSummaryStatistics() { }
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/**
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* Constructs a non-empty instance with the specified {@code count},
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* {@code min}, {@code max}, and {@code sum}.
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*
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* <p>If {@code count} is zero then the remaining arguments are ignored and
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* an empty instance is constructed.
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*
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* <p>If the arguments are inconsistent then an {@code IllegalArgumentException}
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* is thrown. The necessary consistent argument conditions are:
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* <ul>
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* <li>{@code count >= 0}</li>
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* <li>{@code (min <= max && !isNaN(sum)) || (isNaN(min) && isNaN(max) && isNaN(sum))}</li>
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* </ul>
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* @apiNote
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* The enforcement of argument correctness means that the retrieved set of
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* recorded values obtained from a {@code DoubleSummaryStatistics} source
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* instance may not be a legal set of arguments for this constructor due to
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* arithmetic overflow of the source's recorded count of values.
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* The consistent argument conditions are not sufficient to prevent the
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* creation of an internally inconsistent instance. An example of such a
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* state would be an instance with: {@code count} = 2, {@code min} = 1,
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* {@code max} = 2, and {@code sum} = 0.
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*
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* @param count the count of values
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* @param min the minimum value
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* @param max the maximum value
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* @param sum the sum of all values
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* @throws IllegalArgumentException if the arguments are inconsistent
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* @since 10
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*/
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public DoubleSummaryStatistics(long count, double min, double max, double sum)
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throws IllegalArgumentException {
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if (count < 0L) {
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throw new IllegalArgumentException("Negative count value");
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} else if (count > 0L) {
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if (min > max)
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throw new IllegalArgumentException("Minimum greater than maximum");
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// All NaN or non NaN
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var ncount = DoubleStream.of(min, max, sum).filter(Double::isNaN).count();
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if (ncount > 0 && ncount < 3)
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throw new IllegalArgumentException("Some, not all, of the minimum, maximum, or sum is NaN");
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this.count = count;
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this.sum = sum;
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this.simpleSum = sum;
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this.sumCompensation = 0.0d;
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this.min = min;
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this.max = max;
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}
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// Use default field values if count == 0
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}
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/**
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* Records another value into the summary information.
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*
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* @param value the input value
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*/
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@Override
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public void accept(double value) {
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++count;
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simpleSum += value;
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sumWithCompensation(value);
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min = Math.min(min, value);
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max = Math.max(max, value);
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}
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/**
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* Combines the state of another {@code DoubleSummaryStatistics} into this
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* one.
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*
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* @param other another {@code DoubleSummaryStatistics}
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* @throws NullPointerException if {@code other} is null
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*/
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public void combine(DoubleSummaryStatistics other) {
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count += other.count;
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simpleSum += other.simpleSum;
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sumWithCompensation(other.sum);
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// Subtract compensation bits
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sumWithCompensation(-other.sumCompensation);
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min = Math.min(min, other.min);
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max = Math.max(max, other.max);
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}
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/**
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* Incorporate a new double value using Kahan summation /
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* compensated summation.
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*/
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private void sumWithCompensation(double value) {
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double tmp = value - sumCompensation;
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double velvel = sum + tmp; // Little wolf of rounding error
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sumCompensation = (velvel - sum) - tmp;
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sum = velvel;
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}
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/**
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* Return the count of values recorded.
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*
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* @return the count of values
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*/
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public final long getCount() {
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return count;
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}
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/**
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* Returns the sum of values recorded, or zero if no values have been
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* recorded.
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*
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* <p> The value of a floating-point sum is a function both of the
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* input values as well as the order of addition operations. The
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* order of addition operations of this method is intentionally
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* not defined to allow for implementation flexibility to improve
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* the speed and accuracy of the computed result.
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*
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* In particular, this method may be implemented using compensated
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* summation or other technique to reduce the error bound in the
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* numerical sum compared to a simple summation of {@code double}
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* values.
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*
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* Because of the unspecified order of operations and the
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* possibility of using differing summation schemes, the output of
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* this method may vary on the same input values.
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*
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* <p>Various conditions can result in a non-finite sum being
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* computed. This can occur even if the all the recorded values
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* being summed are finite. If any recorded value is non-finite,
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* the sum will be non-finite:
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*
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* <ul>
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*
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* <li>If any recorded value is a NaN, then the final sum will be
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* NaN.
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*
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* <li>If the recorded values contain one or more infinities, the
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* sum will be infinite or NaN.
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*
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* <ul>
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*
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* <li>If the recorded values contain infinities of opposite sign,
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* the sum will be NaN.
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*
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* <li>If the recorded values contain infinities of one sign and
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* an intermediate sum overflows to an infinity of the opposite
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* sign, the sum may be NaN.
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*
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* </ul>
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*
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* </ul>
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*
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* It is possible for intermediate sums of finite values to
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* overflow into opposite-signed infinities; if that occurs, the
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* final sum will be NaN even if the recorded values are all
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* finite.
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*
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* If all the recorded values are zero, the sign of zero is
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* <em>not</em> guaranteed to be preserved in the final sum.
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*
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* @apiNote Values sorted by increasing absolute magnitude tend to yield
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* more accurate results.
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*
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* @return the sum of values, or zero if none
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*/
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public final double getSum() {
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// Better error bounds to add both terms as the final sum
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double tmp = sum - sumCompensation;
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if (Double.isNaN(tmp) && Double.isInfinite(simpleSum))
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// If the compensated sum is spuriously NaN from
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// accumulating one or more same-signed infinite values,
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// return the correctly-signed infinity stored in
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// simpleSum.
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return simpleSum;
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else
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return tmp;
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}
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/**
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* Returns the minimum recorded value, {@code Double.NaN} if any recorded
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* value was NaN or {@code Double.POSITIVE_INFINITY} if no values were
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* recorded. Unlike the numerical comparison operators, this method
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* considers negative zero to be strictly smaller than positive zero.
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*
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* @return the minimum recorded value, {@code Double.NaN} if any recorded
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* value was NaN or {@code Double.POSITIVE_INFINITY} if no values were
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* recorded
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*/
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public final double getMin() {
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return min;
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}
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/**
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* Returns the maximum recorded value, {@code Double.NaN} if any recorded
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* value was NaN or {@code Double.NEGATIVE_INFINITY} if no values were
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* recorded. Unlike the numerical comparison operators, this method
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* considers negative zero to be strictly smaller than positive zero.
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*
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* @return the maximum recorded value, {@code Double.NaN} if any recorded
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* value was NaN or {@code Double.NEGATIVE_INFINITY} if no values were
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* recorded
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*/
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public final double getMax() {
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return max;
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}
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/**
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* Returns the arithmetic mean of values recorded, or zero if no
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* values have been recorded.
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*
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* <p> The computed average can vary numerically and have the
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* special case behavior as computing the sum; see {@link #getSum}
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* for details.
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*
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* @apiNote Values sorted by increasing absolute magnitude tend to yield
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* more accurate results.
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*
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* @return the arithmetic mean of values, or zero if none
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*/
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public final double getAverage() {
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return getCount() > 0 ? getSum() / getCount() : 0.0d;
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}
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/**
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* Returns a non-empty string representation of this object suitable for
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* debugging. The exact presentation format is unspecified and may vary
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* between implementations and versions.
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*/
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@Override
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public String toString() {
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return String.format(
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"%s{count=%d, sum=%f, min=%f, average=%f, max=%f}",
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this.getClass().getSimpleName(),
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getCount(),
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getSum(),
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getMin(),
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getAverage(),
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getMax());
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}
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}
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