[calc-percentile] calc percentile
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=========
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### Relevant articles:
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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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<modelVersion>4.0.0</modelVersion>
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<artifactId>core-java-lang-math-4</artifactId>
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<name>core-java-lang-math-4</name>
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<parent>
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<groupId>com.baeldung.core-java-modules</groupId>
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<artifactId>core-java-modules</artifactId>
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<version>0.0.1-SNAPSHOT</version>
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</parent>
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</project>
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package com.baeldung.percentile;
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import static org.junit.jupiter.api.Assertions.assertEquals;
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import static org.junit.jupiter.api.Assertions.assertThrows;
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import java.util.Arrays;
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import java.util.Collection;
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import java.util.Collections;
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import java.util.List;
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import java.util.stream.Collectors;
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import java.util.stream.IntStream;
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import java.util.stream.LongStream;
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import org.junit.jupiter.api.Test;
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public class CalculatePercentileUnitTest {
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public static <T extends Comparable<T>> T getPercentile(Collection<T> input, double percentile) {
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if (input == null || input.isEmpty()) {
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throw new IllegalArgumentException("The input dataset cannot be null or empty.");
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}
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if (percentile < 0 || percentile > 100) {
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throw new IllegalArgumentException("Percentile must be between 0 and 100(exclusive)");
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}
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List<T> sortedList = input.stream()
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.sorted()
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.collect(Collectors.toList());
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int rank = percentile == 0 ? 1 : (int) Math.ceil(percentile / 100.0 * input.size());
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return sortedList.get(rank - 1);
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}
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@Test
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void whenCallingGetPercentileWithAList_thenGetExpectedResult() {
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assertThrows(IllegalArgumentException.class, () -> getPercentile(List.of(1, 2, 3), -1));
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assertThrows(IllegalArgumentException.class, () -> getPercentile(List.of(1, 2, 3), 101));
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List<Integer> list100 = IntStream.rangeClosed(1, 100)
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.boxed()
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.collect(Collectors.toList());
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Collections.shuffle(list100);
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assertEquals(10, getPercentile(list100, 10));
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assertEquals(25, getPercentile(list100, 25));
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assertEquals(50, getPercentile(list100, 50));
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assertEquals(76, getPercentile(list100, 75.3));
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List<Integer> list8 = IntStream.of(-1, 200, 30, 42, -5, 7, 8, 92)
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.boxed()
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.collect(Collectors.toList());
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assertEquals(-5, getPercentile(list8, 10));
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assertEquals(-1, getPercentile(list8, 25));
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assertEquals(8, getPercentile(list8, 50));
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assertEquals(92, getPercentile(list8, 75.3));
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}
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@Test
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void whenCallingGetPercentileWithAnArray_thenGetExpectedResult() {
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//prepare the input array
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long[] theArray = LongStream.of(-1, 200, 30, 42, -5, 7, 8, 92)
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.toArray();
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//convert the long[] array to a List<Long>
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List<Long> list8 = Arrays.stream(theArray)
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.boxed()
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.toList();
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assertEquals(-5, getPercentile(list8, 10));
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assertEquals(-1, getPercentile(list8, 25));
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assertEquals(8, getPercentile(list8, 50));
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assertEquals(92, getPercentile(list8, 75.3));
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}
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}
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