public class Skewness extends AbstractStorelessUnivariateStatistic implements Serializable
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 statistic is undefined for n < 3. Double.Nan
is returned when there is not sufficient data to compute the statistic.
Double.NaN may also be returned if the input includes NaN and / or
infinite values.
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.
Modifier and Type | Field and Description |
---|---|
protected boolean |
incMoment
Determines whether or not this statistic can be incremented or cleared.
|
protected org.apache.commons.math3.stat.descriptive.moment.ThirdMoment |
moment
Third moment on which this statistic is based
|
Constructor and Description |
---|
Skewness()
Constructs a Skewness
|
Skewness(Skewness original)
Copy constructor, creates a new
Skewness identical
to the original |
Skewness(org.apache.commons.math3.stat.descriptive.moment.ThirdMoment m3)
Constructs a Skewness with an external moment
|
Modifier and Type | Method and Description |
---|---|
void |
clear()
Clears the internal state of the Statistic
|
Skewness |
copy()
Returns a copy of the statistic with the same internal state.
|
static void |
copy(Skewness source,
Skewness dest)
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 |
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.
|
equals, evaluate, hashCode, incrementAll, incrementAll
evaluate, getData, getDataRef, setData, setData, test, test, test, test
protected org.apache.commons.math3.stat.descriptive.moment.ThirdMoment moment
protected boolean incMoment
Statistics based on (constructed from) external moments cannot be incremented or cleared.
public Skewness()
public Skewness(org.apache.commons.math3.stat.descriptive.moment.ThirdMoment m3)
m3
- external momentpublic Skewness(Skewness original) throws NullArgumentException
Skewness
identical
to the original
original
- the Skewness
instance to copyNullArgumentException
- if original is nullpublic void increment(double d)
Note that when Skewness(ThirdMoment)
is used to
create a Skewness, this method does nothing. In that case, the
ThirdMoment should be incremented directly.
increment
in interface StorelessUnivariateStatistic
increment
in class AbstractStorelessUnivariateStatistic
d
- the new value.public double getResult()
See Skewness
for the definition used in the computation.
getResult
in interface StorelessUnivariateStatistic
getResult
in class AbstractStorelessUnivariateStatistic
public long getN()
getN
in interface StorelessUnivariateStatistic
public void clear()
clear
in interface StorelessUnivariateStatistic
clear
in class AbstractStorelessUnivariateStatistic
public double evaluate(double[] values, int begin, int length) throws MathIllegalArgumentException
See Skewness
for the definition used in the computation.
Throws IllegalArgumentException
if the array is null.
evaluate
in interface UnivariateStatistic
evaluate
in interface MathArrays.Function
evaluate
in class AbstractStorelessUnivariateStatistic
values
- the input arraybegin
- the index of the first array element to includelength
- the number of elements to includeMathIllegalArgumentException
- if the array is null or the array index
parameters are not validUnivariateStatistic.evaluate(double[], int, int)
public Skewness copy()
copy
in interface StorelessUnivariateStatistic
copy
in interface UnivariateStatistic
copy
in class AbstractStorelessUnivariateStatistic
public static void copy(Skewness source, Skewness dest) throws NullArgumentException
Neither source nor dest can be null.
source
- Skewness to copydest
- Skewness to copy toNullArgumentException
- if either source or dest is nullCopyright © 2003–2016 The Apache Software Foundation. All rights reserved.