Class Skewness
java.lang.Object
org.apache.commons.math.stat.descriptive.AbstractUnivariateStatistic
org.apache.commons.math.stat.descriptive.AbstractStorelessUnivariateStatistic
org.apache.commons.math.stat.descriptive.moment.Skewness
- All Implemented Interfaces:
Serializable
,StorelessUnivariateStatistic
,UnivariateStatistic
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.
- Version:
- $Revision: 1006299 $ $Date: 2010-10-10 16:47:17 +0200 (dim. 10 oct. 2010) $
- See Also:
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Field Summary
FieldsModifier and TypeFieldDescriptionprotected boolean
Determines whether or not this statistic can be incremented or cleared.protected ThirdMoment
Third moment on which this statistic is based -
Constructor Summary
ConstructorsConstructorDescriptionSkewness()
Constructs a SkewnessCopy constructor, creates a newSkewness
identical to theoriginal
Skewness
(ThirdMoment m3) Constructs a Skewness with an external moment -
Method Summary
Modifier and TypeMethodDescriptionvoid
clear()
Clears the internal state of the Statisticcopy()
Returns a copy of the statistic with the same internal state.static void
Copies source to dest.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
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
evaluate, getData, getDataRef, setData, setData, test, test
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Field Details
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moment
Third moment on which this statistic is based -
incMoment
protected boolean incMomentDetermines whether or not this statistic can be incremented or cleared.Statistics based on (constructed from) external moments cannot be incremented or cleared.
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Constructor Details
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Skewness
public Skewness()Constructs a Skewness -
Skewness
Constructs a Skewness with an external moment- Parameters:
m3
- external moment
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Skewness
Copy constructor, creates a newSkewness
identical to theoriginal
- Parameters:
original
- theSkewness
instance to copy
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Method Details
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increment
public void increment(double d) Updates the internal state of the statistic to reflect the addition of the new value.- Specified by:
increment
in interfaceStorelessUnivariateStatistic
- Specified by:
increment
in classAbstractStorelessUnivariateStatistic
- Parameters:
d
- the new value.
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getResult
public double getResult()Returns the value of the statistic based on the values that have been added.See
Skewness
for the definition used in the computation.- Specified by:
getResult
in interfaceStorelessUnivariateStatistic
- Specified by:
getResult
in classAbstractStorelessUnivariateStatistic
- Returns:
- the skewness of the available values.
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getN
public long getN()Returns the number of values that have been added.- Specified by:
getN
in interfaceStorelessUnivariateStatistic
- Returns:
- the number of values.
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clear
public void clear()Clears the internal state of the Statistic- Specified by:
clear
in interfaceStorelessUnivariateStatistic
- Specified by:
clear
in classAbstractStorelessUnivariateStatistic
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evaluate
public double evaluate(double[] values, int begin, int length) Returns the Skewness of the entries in the specifed portion of the input array.See
Skewness
for the definition used in the computation.Throws
IllegalArgumentException
if the array is null.- Specified by:
evaluate
in interfaceUnivariateStatistic
- Overrides:
evaluate
in classAbstractStorelessUnivariateStatistic
- Parameters:
values
- the input arraybegin
- the index of the first array element to includelength
- the number of elements to include- Returns:
- the skewness of the values or Double.NaN if length is less than 3
- Throws:
IllegalArgumentException
- if the array is null or the array index parameters are not valid- See Also:
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copy
Returns a copy of the statistic with the same internal state.- Specified by:
copy
in interfaceStorelessUnivariateStatistic
- Specified by:
copy
in interfaceUnivariateStatistic
- Specified by:
copy
in classAbstractStorelessUnivariateStatistic
- Returns:
- a copy of the statistic
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copy
Copies source to dest.Neither source nor dest can be null.
- Parameters:
source
- Skewness to copydest
- Skewness to copy to- Throws:
NullPointerException
- if either source or dest is null
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