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From "Carl Witt (JIRA)" <j...@apache.org>
Subject [jira] [Created] (MATH-1129) Percentile Computation errs
Date Tue, 17 Jun 2014 09:24:01 GMT
Carl Witt created MATH-1129:
-------------------------------

             Summary: Percentile Computation errs
                 Key: MATH-1129
                 URL: https://issues.apache.org/jira/browse/MATH-1129
             Project: Commons Math
          Issue Type: Bug
    Affects Versions: 3.2
         Environment: Java 1.8.0
            Reporter: Carl Witt


In the following test, the 75th percentile is _smaller_ than the 25th percentile, leaving
me with a negative interquartile range.

{code:title=Bar.java|borderStyle=solid}
@Test public void negativePercentiles(){

        double[] data = new double[]{
                -0.012086732064244697, 
                -0.24975668704012527, 
                0.5706168483164684, 
                -0.322111769955327, 
                0.24166759508327315, 
                Double.NaN, 
                0.16698443218942854, 
                -0.10427763937565114, 
                -0.15595963093172435, 
                -0.028075857595882995, 
                -0.24137994506058857, 
                0.47543170476574426, 
                -0.07495595384947631, 
                0.37445697625436497, 
                -0.09944199541668033
        };
        DescriptiveStatistics descriptiveStatistics = new DescriptiveStatistics(data);

        double threeQuarters = descriptiveStatistics.getPercentile(75);
        double oneQuarter = descriptiveStatistics.getPercentile(25);

        double IQR = threeQuarters - oneQuarter;
        
        System.out.println(String.format("25th percentile %s 75th percentile %s", oneQuarter,
threeQuarters ));
        
        assert IQR >= 0;
        
    }
{code}



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