[calc-percentile] calc percentile

core-java-modules/core-java-lang-math-4/README.md

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+=========
+
+### Relevant articles:

core-java-modules/core-java-lang-math-4/pom.xml

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+<?xml version="1.0" encoding="UTF-8"?>
+<project xmlns="http://maven.apache.org/POM/4.0.0"
+    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+    xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
+    <modelVersion>4.0.0</modelVersion>
+    <artifactId>core-java-lang-math-4</artifactId>
+    <name>core-java-lang-math-4</name>
+
+    <parent>
+        <groupId>com.baeldung.core-java-modules</groupId>
+        <artifactId>core-java-modules</artifactId>
+        <version>0.0.1-SNAPSHOT</version>
+    </parent>
+
+</project>

core-java-modules/core-java-lang-math-4/src/test/java/com/baeldung/percentile/CalculatePercentileUnitTest.java

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