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java.lang.Objectorg.apache.commons.math.stat.descriptive.AbstractUnivariateStatistic
org.apache.commons.math.stat.descriptive.AbstractStorelessUnivariateStatistic
org.apache.commons.math.stat.descriptive.moment.Skewness
public class Skewness
Computes the skewness of the available values.
We use the following (unbiased) formula to define skewness:
skewness = [n / (n -1) (n - 2)] sum[(x_i - mean)^3] / std^3
where n is the number of values, mean is the Mean
and std is the
StandardDeviation
Note that this implementation is not synchronized. If
multiple threads access an instance of this class concurrently, and at least
one of the threads invokes the increment()
or
clear()
method, it must be synchronized externally.
Field Summary | |
---|---|
protected boolean |
incMoment
Determines whether or not this statistic can be incremented or cleared. |
protected ThirdMoment |
moment
Third moment on which this statistic is based |
Constructor Summary | |
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Skewness()
Constructs a Skewness |
|
Skewness(ThirdMoment m3)
Constructs a Skewness with an external moment |
Method Summary | |
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void |
clear()
Clears the internal state of the Statistic |
double |
evaluate(double[] values,
int begin,
int length)
Returns the Skewness of the entries in the specifed portion of the input array. |
long |
getN()
Returns the number of values that have been added. |
double |
getResult()
Returns the value of the statistic based on the values that have been added. |
void |
increment(double d)
Updates the internal state of the statistic to reflect the addition of the new value. |
Methods inherited from class org.apache.commons.math.stat.descriptive.AbstractStorelessUnivariateStatistic |
---|
equals, evaluate, hashCode, incrementAll, incrementAll |
Methods inherited from class org.apache.commons.math.stat.descriptive.AbstractUnivariateStatistic |
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test |
Methods inherited from class java.lang.Object |
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clone, finalize, getClass, notify, notifyAll, toString, wait, wait, wait |
Field Detail |
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protected ThirdMoment moment
protected boolean incMoment
Statistics based on (constructed from) external moments cannot be incremented or cleared.
Constructor Detail |
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public Skewness()
public Skewness(ThirdMoment m3)
m3
- external momentMethod Detail |
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public void increment(double d)
StorelessUnivariateStatistic
increment
in interface StorelessUnivariateStatistic
increment
in class AbstractStorelessUnivariateStatistic
d
- the new value.StorelessUnivariateStatistic.increment(double)
public double getResult()
See Skewness
for the definition used in the computation.
getResult
in interface StorelessUnivariateStatistic
getResult
in class AbstractStorelessUnivariateStatistic
StorelessUnivariateStatistic.getResult()
public long getN()
StorelessUnivariateStatistic
getN
in interface StorelessUnivariateStatistic
StorelessUnivariateStatistic.getN()
public void clear()
StorelessUnivariateStatistic
clear
in interface StorelessUnivariateStatistic
clear
in class AbstractStorelessUnivariateStatistic
StorelessUnivariateStatistic.clear()
public double evaluate(double[] values, int begin, int length)
See Skewness
for the definition used in the computation.
Throws IllegalArgumentException
if the array is null.
evaluate
in interface UnivariateStatistic
evaluate
in class AbstractStorelessUnivariateStatistic
values
- the input arraybegin
- the index of the first array element to includelength
- the number of elements to include
IllegalArgumentException
- if the array is null or the array index
parameters are not validUnivariateStatistic.evaluate(double[], int, int)
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