001 /*
002 * Java Genetic Algorithm Library (jenetics-3.7.0).
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.IntConsumer;
027 import java.util.function.ToIntFunction;
028 import java.util.stream.Collector;
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 * design of the {@link java.util.IntSummaryStatistics} 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 ints with:
037 * <pre>{@code
038 * final IntStream stream = ...
039 * final IntMomentStatistics statistics = stream.collect(
040 * IntMomentStatistics::new,
041 * IntMomentStatistics::accept,
042 * IntMomentStatistics::combine
043 * );
044 * }</pre>
045 *
046 * For a non int stream, you can use a collector:
047 * <pre>{@code
048 * final Stream<SomeObject> stream = ...
049 * final IntMomentStatistics statistics = stream
050 * .collect(toIntMomentStatistics(v -> v.intValue()));
051 * }</pre>
052 *
053 * <p>
054 * <b>Implementation note:</b>
055 * <i>This implementation is not thread safe. However, it is safe to use
056 * {@link #toIntMomentStatistics(ToIntFunction)} on a parallel stream, because the parallel
057 * implementation of {@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.</i>
060 *
061 * @see java.util.IntSummaryStatistics
062 * @see org.jenetics.stat.IntMoments
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@gmx.at">Franz Wilhelmstötter</a>
067 * @since 3.0
068 * @version 3.7
069 */
070 public class IntMomentStatistics
071 extends MomentStatistics
072 implements IntConsumer
073 {
074
075 private int _min = Integer.MAX_VALUE;
076 private int _max = Integer.MIN_VALUE;
077 private long _sum = 0L;
078
079 /**
080 * Create an empty moments object.
081 */
082 public IntMomentStatistics() {
083 }
084
085 /**
086 * Records a new value into the moments information
087 *
088 * @param value the input {@code value}
089 */
090 @Override
091 public void accept(final int value) {
092 super.accept(value);
093 _min = min(_min, value);
094 _max = max(_max, value);
095 _sum += value;
096 }
097
098 /**
099 * Combine two {@code IntMoments} statistic objects.
100 *
101 * @param other the other {@code IntMoments} statistics to combine with
102 * {@code this} one.
103 * @return {@code this} statistics object
104 * @throws java.lang.NullPointerException if the other statistical summary
105 * is {@code null}.
106 */
107 public IntMomentStatistics combine(final IntMomentStatistics other) {
108 super.combine(other);
109 _min = min(_min, other._min);
110 _max = max(_max, other._max);
111 _sum += other._sum;
112
113 return this;
114 }
115
116 /**
117 * Return the minimum value recorded, or {@code Integer.MAX_VALUE} if no
118 * values have been recorded.
119 *
120 * @return the minimum value, or {@code Integer.MAX_VALUE} if none
121 */
122 public int getMin() {
123 return _min;
124 }
125
126 /**
127 * Return the maximum value recorded, or {@code Integer.MIN_VALUE} if no
128 * values have been recorded.
129 *
130 * @return the maximum value, or {@code Integer.MIN_VALUE} if none
131 */
132 public int getMax() {
133 return _max;
134 }
135
136 /**
137 * Return the sum of values recorded, or zero if no values have been
138 * recorded.
139 *
140 * @return the sum of values, or zero if none
141 */
142 public long getSum() {
143 return _sum;
144 }
145
146 /**
147 * Compares the state of two {@code IntMomentStatistics} objects. This is
148 * a replacement for the {@link #equals(Object)} which is not advisable to
149 * implement for this mutable object. If two object have the same state, it
150 * has still the same state when updated with the same value.
151 * <pre>{@code
152 * final IntMomentStatistics ims1 = ...;
153 * final IntMomentStatistics ims2 = ...;
154 *
155 * if (ims1.sameState(ims2)) {
156 * final int value = random.nextInt(1_000_000);
157 * ims1.accept(value);
158 * ims2.accept(value);
159 *
160 * assert ims1.sameState(ims2);
161 * assert ims2.sameState(ims1);
162 * assert ims1.sameState(ims1);
163 * }
164 * }</pre>
165 *
166 * @since 3.7
167 *
168 * @param other the other object for the test
169 * @return {@code true} the {@code this} and the {@code other} objects have
170 * the same state, {@code false} otherwise
171 */
172 public boolean sameState(final IntMomentStatistics other) {
173 return _min == other._min &&
174 _max == other._max &&
175 _sum == other._sum &&
176 super.sameState(other);
177 }
178
179 @Override
180 public String toString() {
181 return String.format(
182 "IntMomentStatistics[N=%d, ∧=%s, ∨=%s, Σ=%s, μ=%s, s²=%s, S=%s, K=%s]",
183 getCount(), getMin(), getMax(), getSum(),
184 getMean(), getVariance(), getSkewness(), getKurtosis()
185 );
186 }
187
188 /**
189 * Return a {@code Collector} which applies an int-producing mapping
190 * function to each input element, and returns moments-statistics for the
191 * resulting values.
192 *
193 * <pre>{@code
194 * final Stream<SomeObject> stream = ...
195 * final IntMomentStatistics statistics = stream
196 * .collect(toIntMomentStatistics(v -> v.intValue()));
197 * }</pre>
198 *
199 * @param mapper a mapping function to apply to each element
200 * @param <T> the type of the input elements
201 * @return a {@code Collector} implementing the moments-statistics reduction
202 * @throws java.lang.NullPointerException if the given {@code mapper} is
203 * {@code null}
204 */
205 public static <T> Collector<T, ?, IntMomentStatistics>
206 toIntMomentStatistics(final ToIntFunction<? super T> mapper) {
207 requireNonNull(mapper);
208 return Collector.of(
209 IntMomentStatistics::new,
210 (r, t) -> r.accept(mapper.applyAsInt(t)),
211 IntMomentStatistics::combine
212 );
213 }
214
215 }
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