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Add different types of Mean (#4339)
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‎pom.xml

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<?xml version="1.0" encoding="UTF-8"?>
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<project xmlns="http://maven.apache.org/POM/4.0.0"
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xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
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xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
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xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
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xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
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<modelVersion>4.0.0</modelVersion>
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<groupId>com.thealgorithms</groupId>
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<artifactId>Java</artifactId>
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<artifactId>commons-lang3</artifactId>
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<version>3.12.0</version>
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</dependency>
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<dependency>
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<groupId>org.apache.commons</groupId>
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<artifactId>commons-collections4</artifactId>
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<version>4.4</version>
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</dependency>
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</dependencies>
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<build>

‎src/main/java/com/thealgorithms/maths/Means.java

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package com.thealgorithms.maths;
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import java.util.stream.StreamSupport;
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import org.apache.commons.collections4.IterableUtils;
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/**
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* https://en.wikipedia.org/wiki/Mean
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* <p>
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* by: Punit Patel
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*/
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public final class Means {
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private Means() {
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}
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/**
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* @brief computes the [Arithmetic Mean](https://en.wikipedia.org/wiki/Arithmetic_mean) of the input
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* @param numbers the input numbers
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* @throws IllegalArgumentException empty input
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* @return the arithmetic mean of the input numbers
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*/
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public static Double arithmetic(final Iterable<Double> numbers) {
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checkIfNotEmpty(numbers);
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return StreamSupport.stream(numbers.spliterator(), false).reduce((x, y) -> x + y).get() / IterableUtils.size(numbers);
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}
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/**
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* @brief computes the [Geometric Mean](https://en.wikipedia.org/wiki/Geometric_mean) of the input
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* @param numbers the input numbers
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* @throws IllegalArgumentException empty input
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* @return the geometric mean of the input numbers
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*/
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public static Double geometric(final Iterable<Double> numbers) {
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checkIfNotEmpty(numbers);
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return Math.pow(StreamSupport.stream(numbers.spliterator(), false).reduce((x, y) -> x * y).get(), 1d / IterableUtils.size(numbers));
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}
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/**
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* @brief computes the [Harmonic Mean](https://en.wikipedia.org/wiki/Harmonic_mean) of the input
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* @param numbers the input numbers
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* @throws IllegalArgumentException empty input
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* @return the harmonic mean of the input numbers
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*/
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public static Double harmonic(final Iterable<Double> numbers) {
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checkIfNotEmpty(numbers);
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return IterableUtils.size(numbers) / StreamSupport.stream(numbers.spliterator(), false).reduce(0d, (x, y) -> x + 1d / y);
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}
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private static void checkIfNotEmpty(final Iterable<Double> numbers) {
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if (!numbers.iterator().hasNext()) {
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throw new IllegalArgumentException("Emtpy list given for Mean computation.");
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}
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}
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}

‎src/test/java/com/thealgorithms/maths/MeansTest.java

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package com.thealgorithms.maths;
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import static org.junit.jupiter.api.Assertions.*;
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import java.util.ArrayList;
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import java.util.LinkedHashSet;
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import java.util.LinkedList;
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import java.util.List;
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import java.util.Set;
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import java.util.Vector;
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import org.assertj.core.util.Lists;
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import org.assertj.core.util.Sets;
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import org.junit.jupiter.api.Test;
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class MeansTest {
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@Test
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void arithmeticMeanZeroNumbers() throws IllegalArgumentException {
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List<Double> numbers = new ArrayList<>();
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assertThrows(IllegalArgumentException.class, () -> Means.arithmetic(numbers));
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}
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@Test
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void geometricMeanZeroNumbers() throws IllegalArgumentException {
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List<Double> numbers = new ArrayList<>();
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assertThrows(IllegalArgumentException.class, () -> Means.geometric(numbers));
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}
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@Test
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void harmonicMeanZeroNumbers() throws IllegalArgumentException {
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List<Double> numbers = new ArrayList<>();
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assertThrows(IllegalArgumentException.class, () -> Means.harmonic(numbers));
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}
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@Test
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void arithmeticMeanSingleNumber() {
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List<Double> numbers = Lists.newArrayList(2.5);
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assertEquals(2.5, Means.arithmetic(numbers));
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}
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@Test
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void geometricMeanSingleNumber() {
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Set<Double> numbers = Sets.newHashSet(Lists.newArrayList(2.5));
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assertEquals(2.5, Means.geometric(numbers));
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}
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@Test
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void harmonicMeanSingleNumber() {
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LinkedHashSet<Double> numbers = Sets.newLinkedHashSet(2.5);
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assertEquals(2.5, Means.harmonic(numbers));
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}
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@Test
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void arithmeticMeanMultipleNumbers() {
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Set<Double> numbers = Sets.newTreeSet(1d, 2.5, 83.3, 25.9999, 46.0001, 74.7, 74.5);
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assertEquals(44, Means.arithmetic(numbers));
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}
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@Test
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void geometricMeanMultipleNumbers() {
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LinkedList<Double> numbers = new LinkedList<>() {};
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numbers.addAll(Lists.newArrayList(1d, 2d, 3d, 4d, 5d, 6d, 1.25));
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assertEquals(2.6426195539300585, Means.geometric(numbers));
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}
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@Test
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void harmonicMeanMultipleNumbers() {
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Vector<Double> numbers = new Vector<>(Lists.newArrayList(1d, 2.5, 83.3, 25.9999, 46.0001, 74.7, 74.5));
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assertEquals(4.6697322801074135, Means.harmonic(numbers));
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}
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}

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