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sonar fix: Handle variance=0 in skewness computation for input array

This commit is contained in:
Alex Herbert 2021-08-21 09:11:05 +01:00 committed by Gilles Sadowski
parent 30aa597f1e
commit 5245a685a0
2 changed files with 23 additions and 12 deletions
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30
commons-math-legacy/src/main/java/org/apache/commons/math4/legacy/stat/descriptive/moment/Skewness.java
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@ -49,6 +49,9 @@ public class Skewness extends AbstractStorelessUnivariateStatistic implements Se
/** Serializable version identifier. */ /** Serializable version identifier. */
private static final long serialVersionUID = 20150412L; private static final long serialVersionUID = 20150412L;
/** The value below which the variance is considered zero and thus skewness is zero. */
private static final double ZERO_VARIANCE_THRESHOLD = 10E-20;
/** Third moment on which this statistic is based. */ /** Third moment on which this statistic is based. */
protected ThirdMoment moment; protected ThirdMoment moment;
@ -115,7 +118,7 @@ public class Skewness extends AbstractStorelessUnivariateStatistic implements Se
return Double.NaN; return Double.NaN;
} }
double variance = moment.m2 / (moment.n - 1); double variance = moment.m2 / (moment.n - 1);
if (variance < 10E-20) { if (variance < ZERO_VARIANCE_THRESHOLD) {
return 0.0d; return 0.0d;
} else { } else {
double n0 = moment.getN(); double n0 = moment.getN();
@ -180,19 +183,22 @@ public class Skewness extends AbstractStorelessUnivariateStatistic implements Se
accum2 += d; accum2 += d;
} }
final double variance = (accum - (accum2 * accum2 / length)) / (length - 1); final double variance = (accum - (accum2 * accum2 / length)) / (length - 1);
if (variance < ZERO_VARIANCE_THRESHOLD) {
skew = 0.0d;
} else {
double accum3 = 0.0;
for (int i = begin; i < begin + length; i++) {
final double d = values[i] - m;
accum3 += d * d * d;
}
accum3 /= variance * AccurateMath.sqrt(variance);
double accum3 = 0.0; // Get N
for (int i = begin; i < begin + length; i++) { double n0 = length;
final double d = values[i] - m;
accum3 += d * d * d; // Calculate skewness
skew = (n0 / ((n0 - 1) * (n0 - 2))) * accum3;
} }
accum3 /= variance * AccurateMath.sqrt(variance);
// Get N
double n0 = length;
// Calculate skewness
skew = (n0 / ((n0 - 1) * (n0 - 2))) * accum3;
} }
return skew; return skew;
} }

5
commons-math-legacy/src/test/java/org/apache/commons/math4/legacy/stat/descriptive/moment/SkewnessTest.java
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@ -60,4 +60,9 @@ public class SkewnessTest extends StorelessUnivariateStatisticAbstractTest{
Assert.assertFalse(Double.isNaN(skew.getResult())); Assert.assertFalse(Double.isNaN(skew.getResult()));
} }
@Test
public void testZeroSkewness() {
final double[] values = {2, 2, 2, 2};
Assert.assertEquals(0, new Skewness().evaluate(values), 0.0);
}
} }