Percentile calculation : Document algorithm used

[asfimport]

Aleksei Balan (Bug 61078):
The percentile nearest rank method implemented in JMeter have an error and failing on the data from Wikipedia examples.
https://en.wikipedia.org/wiki/Percentile#The_Nearest_Rank_method

Tests implemented
https://gist.github.com/abalanonline/9b128faa67e2459b765c1ef56454684b

Created attachment TestStatCalculatorPercentile.java: TestStatCalculatorPercentile.java

TestStatCalculatorPercentile.java

package org.apache.jorphan.math;

import org.junit.Before;
import org.junit.Test;

import static org.junit.Assert.assertEquals;

public class TestStatCalculatorPercentile {

    private StatCalculatorLong calc;

    @Before
    public void setUp() {
        calc = new StatCalculatorLong();
    }

    // https://en.wikipedia.org/wiki/Percentile#The_Nearest_Rank_method
    @Test
    public void testPercentileExample1() {
        calc.addValue(15);
        calc.addValue(20);
        calc.addValue(35);
        calc.addValue(40);
        calc.addValue(50);
        assertEquals(15, calc.getPercentPoint(0.05).intValue());
        assertEquals(20, calc.getPercentPoint(0.30).intValue());
        assertEquals(20, calc.getPercentPoint(0.40).intValue());
        assertEquals(35, calc.getPercentPoint(0.50).intValue());
        assertEquals(50, calc.getPercentPoint(1.00).intValue());
    }
    @Test
    public void testPercentileExample2() {
        calc.addValue(3);
        calc.addValue(6);
        calc.addValue(7);
        calc.addValue(8);
        calc.addValue(8);
        calc.addValue(10);
        calc.addValue(13);
        calc.addValue(15);
        calc.addValue(16);
        calc.addValue(20);
        assertEquals(7, calc.getPercentPoint(0.25).intValue());
        assertEquals(8, calc.getPercentPoint(0.50).intValue());
        assertEquals(15, calc.getPercentPoint(0.75).intValue());
        assertEquals(20, calc.getPercentPoint(1.00).intValue());
    }
    @Test
    public void testPercentileExample3() {
        calc.addValue(3);
        calc.addValue(6);
        calc.addValue(7);
        calc.addValue(8);
        calc.addValue(8);
        calc.addValue(9);
        calc.addValue(10);
        calc.addValue(13);
        calc.addValue(15);
        calc.addValue(16);
        calc.addValue(20);
        assertEquals(7, calc.getPercentPoint(0.25).intValue());
        assertEquals(9, calc.getPercentPoint(0.50).intValue());
        assertEquals(15, calc.getPercentPoint(0.75).intValue());
        assertEquals(20, calc.getPercentPoint(1.00).intValue());
    }

}

OS: All

Duplicated by:

• Percentile and Median : Document algorithms used #4399

[asfimport]

@pmouawad (migrated from Bugzilla):
It appears issue is not bug.
http://mail-archives.apache.org/mod_mbox/jmeter-dev/201705.mbox/%3C96b69e93f3e23098636fa16e3be50e7f%40internetallee.de%3E

This bug has been marked as a duplicate of #4399

[asfimport]

@pmouawad (migrated from Bugzilla):
This bug has been marked as a duplicate of #4399