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Jenetics - Java Genetic Algorithm Library
There is a newer version: 8.1.0
/*
 * Java Genetic Algorithm Library (jenetics-7.1.2).
 * Copyright (c) 2007-2023 Franz Wilhelmstötter
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 *
 * Author:
 *    Franz Wilhelmstötter ([email protected])
 */
package io.jenetics.stat;

import static java.util.Objects.requireNonNull;

import java.io.Serial;
import java.io.Serializable;
import java.util.function.ToDoubleFunction;
import java.util.stream.Collector;

/**
 * Value objects which contains statistical moments.
 *
 * @see io.jenetics.stat.DoubleMomentStatistics
 *
 * @param count the count of values recorded
 * @param min the minimum value recorded, or {@link Double#POSITIVE_INFINITY} if
 * 	      no values have been recorded.
 * @param max the maximum value recorded, or {@link Double#NEGATIVE_INFINITY} if
 * 	      no values have been recorded
 * @param sum the sum of values recorded, or zero if no values have been
 * 	      recorded
 * @param mean the arithmetic mean of values recorded, or zero if no values have
 * 	      been recorded
 * @param variance the variance of values recorded, or {@link Double#NaN} if no
 * 	      values have been recorded
 * @param skewness the Skewness
 *        of values recorded, or {@link Double#NaN} if less than two values have
 *        been recorded
 * @param kurtosis the Kurtosis
 *        of values recorded, or {@link Double#NaN} if less than four values
 *        have been recorded
 *
 * @author Franz Wilhelmstötter
 * @since 3.0
 * @version 7.0
 */
public record DoubleMoments(
	long count,
	double min,
	double max,
	double sum,
	double mean,
	double variance,
	double skewness,
	double kurtosis
)
	implements Serializable
{

	@Serial
	private static final long serialVersionUID = 2L;

	@Override
	public String toString() {
		return String.format(
			"DoubleMoments[N=%d, ∧=%s, ∨=%s, Σ=%s, μ=%s, s²=%s, S=%s, K=%s]",
			count(), min(), max(), sum(),
			mean(), variance(), skewness(), kurtosis()
		);
	}

	/**
	 * Return a new value object of the statistical moments, currently
	 * represented by the {@code statistics} object.
	 *
	 * @param statistics the creating (mutable) statistics class
	 * @return the statistical moments
	 */
	public static DoubleMoments of(final DoubleMomentStatistics statistics) {
		return new DoubleMoments(
			statistics.count(),
			statistics.min(),
			statistics.max(),
			statistics.sum(),
			statistics.mean(),
			statistics.variance(),
			statistics.skewness(),
			statistics.kurtosis()
		);
	}

	/**
	 * Return a {@code Collector} which returns moments-statistics for the
	 * resulting values.
	 *
	 * {@code
	 * final Stream stream = ...
	 * final DoubleMoments moments = stream.collect(toDoubleMoments()));
	 * }
	 *
	 * @since 4.1
	 *
	 * @param  the type of the input elements
	 * @return a {@code Collector} implementing the moments-statistics reduction
	 */
	public static  Collector
	toDoubleMoments() {
		return toDoubleMoments(Number::doubleValue);
	}

	/**
	 * Return a {@code Collector} which applies an double-producing mapping
	 * function to each input element, and returns moments-statistics for the
	 * resulting values.
	 *
	 * {@code
	 * final Stream stream = ...
	 * final DoubleMoments moments = stream
	 *     .collect(toDoubleMoments(v -> v.doubleValue()));
	 * }
	 *
	 * @param mapper a mapping function to apply to each element
	 * @param  the type of the input elements
	 * @return a {@code Collector} implementing the moments-statistics reduction
	 * @throws java.lang.NullPointerException if the given {@code mapper} is
	 *         {@code null}
	 */
	public static  Collector
	toDoubleMoments(final ToDoubleFunction mapper) {
		requireNonNull(mapper);
		return Collector.of(
			DoubleMomentStatistics::new,
			(a, b) -> a.accept(mapper.applyAsDouble(b)),
			DoubleMomentStatistics::combine,
			DoubleMoments::of
		);
	}

}