001 /*
002 * Java Genetic Algorithm Library (jenetics-4.1.0).
003 * Copyright (c) 2007-2018 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.ToIntFunction;
026 import java.util.stream.Collector;
027
028 /**
029 * A state object for collecting statistics such as count, min, max, sum, mean,
030 * variance, skewness and kurtosis. The design of this class is similar to the
031 * design of the {@link java.util.IntSummaryStatistics} class.
032 * <p>
033 * This class is designed to work with (though does not require) streams. For
034 * example, you can compute moments-statistics on a stream of ints with:
035 * <pre>{@code
036 * final IntStream stream = ...
037 * final IntMomentStatistics statistics = stream.collect(
038 * IntMomentStatistics::new,
039 * IntMomentStatistics::accept,
040 * IntMomentStatistics::combine
041 * );
042 * }</pre>
043 *
044 * For a non int stream, you can use a collector:
045 * <pre>{@code
046 * final Stream<SomeObject> stream = ...
047 * final IntMomentStatistics statistics = stream
048 * .collect(toIntMomentStatistics(v -> v.intValue()));
049 * }</pre>
050 *
051 * @implNote
052 * This implementation is not thread safe. However, it is safe to use
053 * {@link #toIntMomentStatistics(ToIntFunction)} on a parallel stream, because
054 * the parallel implementation of
055 * {@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.IntSummaryStatistics
060 * @see io.jenetics.stat.IntMoments
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 3.7
067 */
068 public class IntMomentStatistics
069 extends MomentStatistics
070 implements IntConsumer
071 {
072
073 private int _min = Integer.MAX_VALUE;
074 private int _max = Integer.MIN_VALUE;
075 private long _sum = 0L;
076
077 /**
078 * Create an empty moments object.
079 */
080 public IntMomentStatistics() {
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 int value) {
090 super.accept(value);
091 _min = Math.min(_min, value);
092 _max = Math.max(_max, value);
093 _sum += value;
094 }
095
096 /**
097 * Combine two {@code IntMoments} statistic objects.
098 *
099 * @param other the other {@code IntMoments} statistics to combine with
100 * {@code this} one.
101 * @return {@code this} statistics object
102 * @throws java.lang.NullPointerException if the other statistical summary
103 * is {@code null}.
104 */
105 public IntMomentStatistics combine(final IntMomentStatistics other) {
106 super.combine(other);
107 _min = Math.min(_min, other._min);
108 _max = Math.max(_max, other._max);
109 _sum += other._sum;
110
111 return this;
112 }
113
114 /**
115 * Return the minimum value recorded, or {@code Integer.MAX_VALUE} if no
116 * values have been recorded.
117 *
118 * @return the minimum value, or {@code Integer.MAX_VALUE} if none
119 */
120 public int getMin() {
121 return _min;
122 }
123
124 /**
125 * Return the maximum value recorded, or {@code Integer.MIN_VALUE} if no
126 * values have been recorded.
127 *
128 * @return the maximum value, or {@code Integer.MIN_VALUE} if none
129 */
130 public int getMax() {
131 return _max;
132 }
133
134 /**
135 * Return the sum of values recorded, or zero if no values have been
136 * recorded.
137 *
138 * @return the sum of values, or zero if none
139 */
140 public long getSum() {
141 return _sum;
142 }
143
144 /**
145 * Compares the state of two {@code IntMomentStatistics} objects. This is
146 * a replacement for the {@link #equals(Object)} which is not advisable to
147 * implement for this mutable object. If two object have the same state, it
148 * has still the same state when updated with the same value.
149 * <pre>{@code
150 * final IntMomentStatistics ims1 = ...;
151 * final IntMomentStatistics ims2 = ...;
152 *
153 * if (ims1.sameState(ims2)) {
154 * final int value = random.nextInt(1_000_000);
155 * ims1.accept(value);
156 * ims2.accept(value);
157 *
158 * assert ims1.sameState(ims2);
159 * assert ims2.sameState(ims1);
160 * assert ims1.sameState(ims1);
161 * }
162 * }</pre>
163 *
164 * @since 3.7
165 *
166 * @param other the other object for the test
167 * @return {@code true} the {@code this} and the {@code other} objects have
168 * the same state, {@code false} otherwise
169 */
170 public boolean sameState(final IntMomentStatistics other) {
171 return _min == other._min &&
172 _max == other._max &&
173 _sum == other._sum &&
174 super.sameState(other);
175 }
176
177 /**
178 * Return an {@code IntMoments} object from the current statistics,
179 *
180 * @since 3.9
181 *
182 * @return an {@code IntMoments} object from the current statistics
183 */
184 public IntMoments toIntMoments() {
185 return IntMoments.of(this);
186 }
187
188 @Override
189 public String toString() {
190 return String.format(
191 "IntMomentStatistics[N=%d, ∧=%s, ∨=%s, Σ=%s, μ=%s, s²=%s, S=%s, K=%s]",
192 getCount(), getMin(), getMax(), getSum(),
193 getMean(), getVariance(), getSkewness(), getKurtosis()
194 );
195 }
196
197 /**
198 * Return a {@code Collector} which applies an int-producing mapping
199 * function to each input element, and returns moments-statistics for the
200 * resulting values.
201 *
202 * <pre>{@code
203 * final Stream<SomeObject> stream = ...
204 * final IntMomentStatistics statistics = stream
205 * .collect(toIntMomentStatistics(v -> v.intValue()));
206 * }</pre>
207 *
208 * @param mapper a mapping function to apply to each element
209 * @param <T> the type of the input elements
210 * @return a {@code Collector} implementing the moments-statistics reduction
211 * @throws java.lang.NullPointerException if the given {@code mapper} is
212 * {@code null}
213 */
214 public static <T> Collector<T, ?, IntMomentStatistics>
215 toIntMomentStatistics(final ToIntFunction<? super T> mapper) {
216 requireNonNull(mapper);
217 return Collector.of(
218 IntMomentStatistics::new,
219 (r, t) -> r.accept(mapper.applyAsInt(t)),
220 IntMomentStatistics::combine
221 );
222 }
223
224 }
|