001 /*
002 * Java Genetic Algorithm Library (jenetics-6.2.0).
003 * Copyright (c) 2007-2021 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.IntConsumer;
025 import java.util.function.LongConsumer;
026 import java.util.function.ToLongFunction;
027 import java.util.stream.Collector;
028
029 /**
030 * A state object for collecting statistics such as count, min, max, sum, mean,
031 * variance, skewness and kurtosis. The design of this class is similar to the
032 * design of the {@link java.util.LongSummaryStatistics} class.
033 * <p>
034 * This class is designed to work with (though does not require) streams. For
035 * example, you can compute moments-statistics on a stream of longs with:
036 * <pre>{@code
037 * final LongStream stream = ...
038 * final LongMomentStatistics statistics = stream.collect(
039 * LongMomentStatistics::new,
040 * LongMomentStatistics::accept,
041 * LongMomentStatistics::combine
042 * );
043 * }</pre>
044 *
045 * For a non long stream, you can use a collector:
046 * <pre>{@code
047 * final Stream<SomeObject> stream = ...
048 * final LongMomentStatistics statistics = stream
049 * .collect(toLongMomentStatistics(v -> v.longValue()));
050 * }</pre>
051 *
052 * @implNote
053 * This implementation is not thread safe. However, it is safe to use
054 * {@link #toLongMomentStatistics(ToLongFunction)} on a parallel stream, because the parallel
055 * implementation of {@link java.util.stream.Stream#collect Stream.collect()}
056 * provides the necessary partitioning, isolation, and merging of results for
057 * safe and efficient parallel execution.
058 *
059 * @see java.util.LongSummaryStatistics
060 * @see io.jenetics.stat.LongMoments
061 * @see <a href="http://people.xiph.org/~tterribe/notes/homs.html">
062 * Computing Higher-Order Moments Online</a>
063 *
064 * @author <a href="mailto:franz.wilhelmstoetter@gmail.com">Franz Wilhelmstötter</a>
065 * @since 3.0
066 * @version 6.0
067 */
068 public class LongMomentStatistics
069 extends MomentStatistics
070 implements LongConsumer, IntConsumer
071 {
072
073 private long _min = Long.MAX_VALUE;
074 private long _max = Long.MIN_VALUE;
075 private long _sum = 0L;
076
077 /**
078 * Create an empty moments object.
079 */
080 public LongMomentStatistics() {
081 }
082
083 /**
084 * Records a new value into the moments information
085 *
086 * @param value the input {@code value}
087 */
088 @Override
089 public void accept(final long value) {
090 super.accept(value);
091 _min = Math.min(_min, value);
092 _max = Math.max(_max, value);
093 _sum += value;
094 }
095
096 /**
097 * Records a new value into the moments information
098 *
099 * @param value the input {@code value}
100 */
101 @Override
102 public void accept(final int value) {
103 accept((long)value);
104 }
105
106 /**
107 * Combine two {@code LongMoments} statistic objects.
108 *
109 * @param other the other {@code LongMoments} statistics to combine with
110 * {@code this} one.
111 * @return {@code this} statistics object
112 * @throws java.lang.NullPointerException if the other statistical summary
113 * is {@code null}.
114 */
115 public LongMomentStatistics combine(final LongMomentStatistics other) {
116 super.combine(other);
117 _min = Math.min(_min, other._min);
118 _max = Math.max(_max, other._max);
119 _sum += other._sum;
120
121 return this;
122 }
123
124 /**
125 * Return the minimum value recorded, or {@code Long.MAX_VALUE} if no
126 * values have been recorded.
127 *
128 * @return the minimum value, or {@code Long.MAX_VALUE} if none
129 */
130 public long min() {
131 return _min;
132 }
133
134 /**
135 * Return the maximum value recorded, or {@code Long.MIN_VALUE} if no
136 * values have been recorded.
137 *
138 * @return the maximum value, or {@code Long.MIN_VALUE} if none
139 */
140 public long max() {
141 return _max;
142 }
143
144 /**
145 * Return the sum of values recorded, or zero if no values have been
146 * recorded.
147 *
148 * @return the sum of values, or zero if none
149 */
150 public long sum() {
151 return _sum;
152 }
153
154 /**
155 * Compares the state of two {@code LongMomentStatistics} objects. This is
156 * a replacement for the {@link #equals(Object)} which is not advisable to
157 * implement for this mutable object. If two object have the same state, it
158 * has still the same state when updated with the same value.
159 * <pre>{@code
160 * final LongMomentStatistics lms1 = ...;
161 * final LongMomentStatistics lms2 = ...;
162 *
163 * if (lms1.sameState(lms2)) {
164 * final long value = random.nextInt(1_000_000);
165 * lms1.accept(value);
166 * lms2.accept(value);
167 *
168 * assert lms1.sameState(lms2);
169 * assert lms2.sameState(lms1);
170 * assert lms1.sameState(lms1);
171 * }
172 * }</pre>
173 *
174 * @since 3.7
175 *
176 * @param other the other object for the test
177 * @return {@code true} the {@code this} and the {@code other} objects have
178 * the same state, {@code false} otherwise
179 */
180 public boolean sameState(final LongMomentStatistics other) {
181 return this == other ||
182 _min == other._min &&
183 _max == other._max &&
184 _sum == other._sum &&
185 super.sameState(other);
186 }
187
188 /**
189 * Return a {@code LongMoments} object from the current statistics,
190 *
191 * @since 3.9
192 *
193 * @return a {@code LongMoments} object from the current statistics
194 */
195 public LongMoments toLongMoments() {
196 return LongMoments.of(this);
197 }
198
199 @Override
200 public String toString() {
201 return String.format(
202 "LongMomentStatistics[N=%d, ∧=%s, ∨=%s, Σ=%s, μ=%s, s²=%s, S=%s, K=%s]",
203 count(), min(), max(), sum(),
204 mean(), variance(), skewness(), kurtosis()
205 );
206 }
207
208 /**
209 * Return a {@code Collector} which applies an long-producing mapping
210 * function to each input element, and returns moments-statistics for the
211 * resulting values.
212 *
213 * <pre>{@code
214 * final Stream<SomeObject> stream = ...
215 * final LongMomentStatistics statistics = stream
216 * .collect(toLongMomentStatistics(v -> v.longValue()));
217 * }</pre>
218 *
219 * @param mapper a mapping function to apply to each element
220 * @param <T> the type of the input elements
221 * @return a {@code Collector} implementing the moments-statistics reduction
222 * @throws java.lang.NullPointerException if the given {@code mapper} is
223 * {@code null}
224 */
225 public static <T> Collector<T, ?, LongMomentStatistics>
226 toLongMomentStatistics(final ToLongFunction<? super T> mapper) {
227 requireNonNull(mapper);
228 return Collector.of(
229 LongMomentStatistics::new,
230 (r, t) -> r.accept(mapper.applyAsLong(t)),
231 LongMomentStatistics::combine
232 );
233 }
234
235 }
|