001 /*
002 * Java Genetic Algorithm Library (jenetics-3.5.0).
003 * Copyright (c) 2007-2016 Franz Wilhelmstötter
004 *
005 * Licensed under the Apache License, Version 2.0 (the "License");
006 * you may not use this file except in compliance with the License.
007 * 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 * Author:
018 * Franz Wilhelmstötter (franz.wilhelmstoetter@gmx.at)
019 */
020 package org.jenetics.stat;
021
022 import static java.lang.Math.max;
023 import static java.lang.Math.min;
024 import static java.util.Objects.requireNonNull;
025
026 import java.util.function.DoubleConsumer;
027 import java.util.function.ToDoubleFunction;
028 import java.util.stream.Collector;
029
030 import org.jenetics.internal.math.DoubleAdder;
031
032 /**
033 * A state object for collecting statistics such as count, min, max, sum, mean,
034 * variance, skewness and kurtosis. The design of this class is similar to the
035 * {@link java.util.DoubleSummaryStatistics} class.
036 * <p>
037 * This class is designed to work with (though does not require) streams. For
038 * example, you can compute moments-statistics on a stream of doubles with:
039 * <pre>{@code
040 * final DoubleStream stream = ...
041 * final DoubleMomentStatistics statistics = stream.collect(
042 * DoubleMomentStatistics::new,
043 * DoubleMomentStatistics::accept,
044 * DoubleMomentStatistics::combine
045 * );
046 * }</pre>
047 *
048 * For a non double stream, you can use a collector:
049 * <pre>{@code
050 * final Stream<SomeObject> stream = ...
051 * final DoubleMomentStatistics statistics = stream
052 * .collect(toDoubleMomentStatistics(v -> v.doubleValue()));
053 * }</pre>
054 *
055 * <p>
056 * <b>Implementation note:</b>
057 * <i>This implementation is not thread safe. However, it is safe to use
058 * {@link #toDoubleMomentStatistics(ToDoubleFunction)} on a parallel stream,
059 * because the parallel implementation of
060 * {@link java.util.stream.Stream#collect Stream.collect()}
061 * provides the necessary partitioning, isolation, and merging of results for
062 * safe and efficient parallel execution.</i>
063 *
064 * @see java.util.DoubleSummaryStatistics
065 * @see org.jenetics.stat.DoubleMoments
066 * @see <a href="http://people.xiph.org/~tterribe/notes/homs.html">
067 * Computing Higher-Order Moments Online</a>
068 *
069 * @author <a href="mailto:franz.wilhelmstoetter@gmx.at">Franz Wilhelmstötter</a>
070 * @since 3.0
071 * @version 3.0
072 */
073 public class DoubleMomentStatistics
074 extends MomentStatistics
075 implements DoubleConsumer
076 {
077
078 private double _min = Double.POSITIVE_INFINITY;
079 private double _max = Double.NEGATIVE_INFINITY;
080
081 private final DoubleAdder _sum = new DoubleAdder();
082
083 /**
084 * Create an empty moments object.
085 */
086 public DoubleMomentStatistics() {
087 }
088
089 /**
090 * Records a new value into the moments information
091 *
092 * @param value the input {@code value}
093 */
094 @Override
095 public void accept(final double value) {
096 super.accept(value);
097 _min = min(_min, value);
098 _max = max(_max, value);
099 _sum.add(value);
100 }
101
102 /**
103 * Combine two {@code DoubleMoments} statistic objects.
104 *
105 * @param other the other {@code DoubleMoments} statistics to combine with
106 * {@code this} one.
107 * @return {@code this} statistics object
108 * @throws java.lang.NullPointerException if the other statistical summary
109 * is {@code null}.
110 */
111 public DoubleMomentStatistics combine(final DoubleMomentStatistics other) {
112 super.combine(other);
113 _min = min(_min, other._min);
114 _max = max(_max, other._max);
115 _sum.add(other._sum);
116
117 return this;
118 }
119
120 /**
121 * Return the minimum value recorded, or {@code Double.POSITIVE_INFINITY} if
122 * no values have been recorded.
123 *
124 * @return the minimum value, or {@code Double.POSITIVE_INFINITY} if none
125 */
126 public double getMin() {
127 return _min;
128 }
129
130 /**
131 * Return the maximum value recorded, or {@code Double.NEGATIVE_INFINITY} if
132 * no values have been recorded.
133 *
134 * @return the maximum value, or {@code Double.NEGATIVE_INFINITY} if none
135 */
136 public double getMax() {
137 return _max;
138 }
139
140 /**
141 * Return the sum of values recorded, or zero if no values have been
142 * recorded.
143 *
144 * @return the sum of values, or zero if none
145 */
146 public double getSum() {
147 return _sum.doubleValue();
148 }
149
150 @Override
151 public String toString() {
152 return String.format(
153 "Summary[N=%d, ∧=%s, ∨=%s, Σ=%s, μ=%s, s²=%s, S=%s, K=%s]",
154 getCount(), _min, _max, _sum.doubleValue(),
155 getMean(), getVariance(), getSkewness(), getKurtosis()
156 );
157 }
158
159 /**
160 * Return a {@code Collector} which applies an double-producing mapping
161 * function to each input element, and returns moments-statistics for the
162 * resulting values.
163 *
164 * <pre>{@code
165 * final Stream<SomeObject> stream = ...
166 * final DoubleMomentStatistics statistics = stream
167 * .collect(toDoubleMomentStatistics(v -> v.doubleValue()));
168 * }</pre>
169 *
170 * @param mapper a mapping function to apply to each element
171 * @param <T> the type of the input elements
172 * @return a {@code Collector} implementing the moments-statistics reduction
173 * @throws java.lang.NullPointerException if the given {@code mapper} is
174 * {@code null}
175 */
176 public static <T> Collector<T, ?, DoubleMomentStatistics>
177 toDoubleMomentStatistics(final ToDoubleFunction<? super T> mapper) {
178 requireNonNull(mapper);
179 return Collector.of(
180 DoubleMomentStatistics::new,
181 (r, t) -> r.accept(mapper.applyAsDouble(t)),
182 DoubleMomentStatistics::combine
183 );
184 }
185
186 }
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