java.lang.Object
- org.apache.commons.math4.legacy.stat.descriptive.AbstractStorelessUnivariateStatistic
- - org.apache.commons.math4.legacy.stat.descriptive.moment.Skewness

All Implemented Interfaces:

MathArrays.Function, StorelessUnivariateStatistic, UnivariateStatistic
```
public class Skewness
extends AbstractStorelessUnivariateStatistic
```
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 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.

Field Summary

Fields
Modifier and Type	Field	Description
`protected boolean`	`incMoment`	Determines whether or not this statistic can be incremented or cleared.
`protected org.apache.commons.math4.legacy.stat.descriptive.moment.ThirdMoment`	`moment`	Third moment on which this statistic is based.

Constructor Summary

Constructors
Constructor	Description
`Skewness()`	Constructs a Skewness.
`Skewness(Skewness original)`	Copy constructor, creates a new `Skewness` identical to the `original`.
`Skewness(org.apache.commons.math4.legacy.stat.descriptive.moment.ThirdMoment m3)`	Constructs a Skewness with an external moment.

Method Summary

All Methods Static Methods Instance Methods Concrete Methods
Modifier and Type	Method	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 specified 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.math4.legacy.stat.descriptive.AbstractStorelessUnivariateStatistic
equals, evaluate, hashCode, incrementAll, incrementAll

Methods inherited from class java.lang.Object
clone, finalize, getClass, notify, notifyAll, toString, wait, wait, wait

- Field Detail
  - moment
```
protected org.apache.commons.math4.legacy.stat.descriptive.moment.ThirdMoment moment
```
    Third moment on which this statistic is based.
  - incMoment
```
protected boolean incMoment
```
    Determines whether or not this statistic can be incremented or cleared.
    Statistics based on (constructed from) external moments cannot be incremented or cleared.
- Constructor Detail
  - Skewness
```
public Skewness()
```
    Constructs a Skewness.
  - Skewness
```
public Skewness(org.apache.commons.math4.legacy.stat.descriptive.moment.ThirdMoment m3)
```
    Constructs a Skewness with an external moment.
    
    Parameters:
    
    m3 - external moment
  - Skewness
```
public Skewness(Skewness original)
         throws NullArgumentException
```
    Copy constructor, creates a new Skewness identical to the original.
    
    Parameters:
    
    original - the Skewness instance to copy
    
    Throws:
    
    NullArgumentException - if original is null
- Method Detail
  - increment
```
public void increment(double d)
```
    Updates the internal state of the statistic to reflect the addition of the new value.
    Note that when Skewness(ThirdMoment) is used to create a Skewness, this method does nothing. In that case, the ThirdMoment should be incremented directly.
    
    Specified by:
    
    increment in interface StorelessUnivariateStatistic
    
    Specified by:
    
    increment in class AbstractStorelessUnivariateStatistic
    
    Parameters:
    
    d - the new value.
  - 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 interface StorelessUnivariateStatistic
    
    Specified by:
    
    getResult in class AbstractStorelessUnivariateStatistic
    
    Returns:
    
    the skewness of the available values.
  - getN
```
public long getN()
```
    Returns the number of values that have been added.
    
    Returns:
    
    the number of values.
  - clear
```
public void clear()
```
    Clears the internal state of the Statistic.
    
    Specified by:
    
    clear in interface StorelessUnivariateStatistic
    
    Specified by:
    
    clear in class AbstractStorelessUnivariateStatistic
  - evaluate
```
public double evaluate(double[] values,
                       int begin,
                       int length)
                throws MathIllegalArgumentException
```
    Returns the Skewness of the entries in the specified 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 interface MathArrays.Function
    
    Specified by:
    
    evaluate in interface UnivariateStatistic
    
    Overrides:
    
    evaluate in class AbstractStorelessUnivariateStatistic
    
    Parameters:
    
    values - the input array
    
    begin - the index of the first array element to include
    
    length - the number of elements to include
    
    Returns:
    
    the skewness of the values or Double.NaN if length is less than 3
    
    Throws:
    
    MathIllegalArgumentException - if the array is null or the array index parameters are not valid
    
    See Also:
    
    UnivariateStatistic.evaluate(double[], int, int)
  - copy
```
public Skewness copy()
```
    Returns a copy of the statistic with the same internal state.
    
    Specified by:
    
    copy in interface StorelessUnivariateStatistic
    
    Specified by:
    
    copy in interface UnivariateStatistic
    
    Specified by:
    
    copy in class AbstractStorelessUnivariateStatistic
    
    Returns:
    
    a copy of the statistic
  - copy
```
public static void copy(Skewness source,
                        Skewness dest)
                 throws NullArgumentException
```
    Copies source to dest.
    Neither source nor dest can be null.
    
    Parameters:
    
    source - Skewness to copy
    
    dest - Skewness to copy to
    
    Throws:
    
    NullArgumentException - if either source or dest is null

Class Skewness

Field Summary

Constructor Summary

Method Summary

Methods inherited from class org.apache.commons.math4.legacy.stat.descriptive.AbstractStorelessUnivariateStatistic

Methods inherited from class java.lang.Object

Field Detail

moment

incMoment

Constructor Detail

Skewness

Skewness

Skewness

Method Detail

increment

getResult

getN

clear

evaluate

copy

copy