001 /*
002 * Java Genetic Algorithm Library (jenetics-5.2.0).
003 * Copyright (c) 2007-2020 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@gmail.com)
019 */
020 package io.jenetics.stat;
021
022 import static java.util.Objects.requireNonNull;
023
024 import java.util.function.DoubleConsumer;
025 import java.util.function.ToDoubleFunction;
026 import java.util.stream.Collector;
027
028 import io.jenetics.internal.math.DoubleAdder;
029
030 /**
031 * A state object for collecting statistics such as count, min, max, sum, mean,
032 * variance, skewness and kurtosis. The design of this class is similar to the
033 * {@link java.util.DoubleSummaryStatistics} class.
034 * <p>
035 * This class is designed to work with (though does not require) streams. For
036 * example, you can compute moments-statistics on a stream of doubles with:
037 * <pre>{@code
038 * final DoubleStream stream = ...
039 * final DoubleMomentStatistics statistics = stream.collect(
040 * DoubleMomentStatistics::new,
041 * DoubleMomentStatistics::accept,
042 * DoubleMomentStatistics::combine
043 * );
044 * }</pre>
045 *
046 * For a non double stream, you can use a collector:
047 * <pre>{@code
048 * final Stream<SomeObject> stream = ...
049 * final DoubleMomentStatistics statistics = stream
050 * .collect(toDoubleMomentStatistics(v -> v.doubleValue()));
051 * }</pre>
052 *
053 * @implNote
054 * This implementation is not thread safe. However, it is safe to use
055 * {@link #toDoubleMomentStatistics(ToDoubleFunction)} on a parallel stream,
056 * because the parallel implementation of
057 * {@link java.util.stream.Stream#collect Stream.collect()}
058 * provides the necessary partitioning, isolation, and merging of results for
059 * safe and efficient parallel execution.
060 *
061 * @see java.util.DoubleSummaryStatistics
062 * @see io.jenetics.stat.DoubleMoments
063 * @see <a href="http://people.xiph.org/~tterribe/notes/homs.html">
064 * Computing Higher-Order Moments Online</a>
065 *
066 * @author <a href="mailto:franz.wilhelmstoetter@gmail.com">Franz Wilhelmstötter</a>
067 * @since 3.0
068 * @version 5.2
069 */
070 public class DoubleMomentStatistics
071 extends MomentStatistics
072 implements DoubleConsumer
073 {
074
075 private double _min = Double.POSITIVE_INFINITY;
076 private double _max = Double.NEGATIVE_INFINITY;
077
078 private final DoubleAdder _sum = new DoubleAdder();
079
080 /**
081 * Create an empty moments object.
082 */
083 public DoubleMomentStatistics() {
084 }
085
086 /**
087 * Records a new value into the moments information
088 *
089 * @param value the input {@code value}
090 */
091 @Override
092 public void accept(final double value) {
093 super.accept(value);
094 _min = Math.min(_min, value);
095 _max = Math.max(_max, value);
096 _sum.add(value);
097 }
098
099 /**
100 * Combine two {@code DoubleMoments} statistic objects.
101 *
102 * @param other the other {@code DoubleMoments} statistics to combine with
103 * {@code this} one.
104 * @return {@code this} statistics object
105 * @throws java.lang.NullPointerException if the other statistical summary
106 * is {@code null}.
107 */
108 public DoubleMomentStatistics combine(final DoubleMomentStatistics other) {
109 super.combine(other);
110 _min = Math.min(_min, other._min);
111 _max = Math.max(_max, other._max);
112 _sum.add(other._sum);
113
114 return this;
115 }
116
117 /**
118 * Return the minimum value recorded, or {@code Double.POSITIVE_INFINITY} if
119 * no values have been recorded.
120 *
121 * @return the minimum value, or {@code Double.POSITIVE_INFINITY} if none
122 */
123 public double min() {
124 return _min;
125 }
126
127 /**
128 * Return the minimum value recorded, or {@code Double.POSITIVE_INFINITY} if
129 * no values have been recorded.
130 *
131 * @return the minimum value, or {@code Double.POSITIVE_INFINITY} if none
132 * @deprecated Use {@link #min()} instead
133 */
134 @Deprecated
135 public double getMin() {
136 return _min;
137 }
138
139 /**
140 * Return the maximum value recorded, or {@code Double.NEGATIVE_INFINITY} if
141 * no values have been recorded.
142 *
143 * @return the maximum value, or {@code Double.NEGATIVE_INFINITY} if none
144 */
145 public double max() {
146 return _max;
147 }
148
149 /**
150 * Return the maximum value recorded, or {@code Double.NEGATIVE_INFINITY} if
151 * no values have been recorded.
152 *
153 * @return the maximum value, or {@code Double.NEGATIVE_INFINITY} if none
154 * @deprecated Use {@link #max()} instead
155 */
156 @Deprecated
157 public double getMax() {
158 return _max;
159 }
160
161 /**
162 * Return the sum of values recorded, or zero if no values have been
163 * recorded.
164 *
165 * @return the sum of values, or zero if none
166 */
167 public double sum() {
168 return _sum.doubleValue();
169 }
170
171 /**
172 * Return the sum of values recorded, or zero if no values have been
173 * recorded.
174 *
175 * @return the sum of values, or zero if none
176 * @deprecated Use {@link #sum()} instead
177 */
178 @Deprecated
179 public double getSum() {
180 return _sum.doubleValue();
181 }
182
183 /**
184 * Compares the state of two {@code DoubleMomentStatistics} objects. This is
185 * a replacement for the {@link #equals(Object)} which is not advisable to
186 * implement for this mutable object. If two object have the same state, it
187 * has still the same state when updated with the same value.
188 * <pre>{@code
189 * final DoubleMomentStatistics ds1 = ...;
190 * final DoubleMomentStatistics ds2 = ...;
191 *
192 * if (ds1.sameState(ds2)) {
193 * final double value = random.nextDouble();
194 * ds1.accept(value);
195 * ds2.accept(value);
196 *
197 * assert ds1.sameState(ds2);
198 * assert ds2.sameState(ds1);
199 * assert ds1.sameState(ds1);
200 * }
201 * }</pre>
202 *
203 * @since 3.7
204 *
205 * @param other the other object for the test
206 * @return {@code true} the {@code this} and the {@code other} objects have
207 * the same state, {@code false} otherwise
208 */
209 public boolean sameState(final DoubleMomentStatistics other) {
210 return this == other ||
211 Double.compare(_min, other._min) == 0 &&
212 Double.compare(_max, other._max) == 0 &&
213 _sum.sameState(other._sum) &&
214 super.sameState(other);
215 }
216
217 /**
218 * Return a {@code DoubleMoments} object from the current statistics,
219 *
220 * @since 3.9
221 *
222 * @return a {@code DoubleMoments} object from the current statistics
223 */
224 public DoubleMoments toDoubleMoments() {
225 return DoubleMoments.of(this);
226 }
227
228 @Override
229 public String toString() {
230 return String.format(
231 "Summary[N=%d, ∧=%s, ∨=%s, Σ=%s, μ=%s, s²=%s, S=%s, K=%s]",
232 count(), _min, _max, _sum.doubleValue(),
233 mean(), variance(), skewness(), kurtosis()
234 );
235 }
236
237 /**
238 * Return a {@code Collector} which applies an double-producing mapping
239 * function to each input element, and returns moments-statistics for the
240 * resulting values.
241 *
242 * <pre>{@code
243 * final Stream<SomeObject> stream = ...
244 * final DoubleMomentStatistics statistics = stream
245 * .collect(toDoubleMomentStatistics(v -> v.doubleValue()));
246 * }</pre>
247 *
248 * @param mapper a mapping function to apply to each element
249 * @param <T> the type of the input elements
250 * @return a {@code Collector} implementing the moments-statistics reduction
251 * @throws java.lang.NullPointerException if the given {@code mapper} is
252 * {@code null}
253 */
254 public static <T> Collector<T, ?, DoubleMomentStatistics>
255 toDoubleMomentStatistics(final ToDoubleFunction<? super T> mapper) {
256 requireNonNull(mapper);
257 return Collector.of(
258 DoubleMomentStatistics::new,
259 (r, t) -> r.accept(mapper.applyAsDouble(t)),
260 DoubleMomentStatistics::combine
261 );
262 }
263
264 }
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