org.apache.commons.math3.stat.descriptive

## Class DescriptiveStatistics

- java.lang.Object
- - org.apache.commons.math3.stat.descriptive.DescriptiveStatistics

All Implemented Interfaces:
  java.io.Serializable, StatisticalSummary

Direct Known Subclasses:
  SynchronizedDescriptiveStatistics

    public class DescriptiveStatistics
    extends java.lang.Object
    implements StatisticalSummary, java.io.Serializable

Maintains a dataset of values of a single variable and computes descriptive statistics based on stored data. The `windowSize` property sets a limit on the number of values that can be stored in the dataset. The default value, INFINITE_WINDOW, puts no limit on the size of the dataset. This value should be used with caution, as the backing store will grow without bound in this case. For very large datasets, `SummaryStatistics`, which does not store the dataset, should be used instead of this class. If `windowSize` is not INFINITE_WINDOW and more values are added than can be stored in the dataset, new values are added in a "rolling" manner, with new values replacing the "oldest" values in the dataset.

Note: this class is not threadsafe. Use `SynchronizedDescriptiveStatistics` if concurrent access from multiple threads is required.

Version:
  $Id: DescriptiveStatistics.java 1422354 2012-12-15 20:59:01Z psteitz $
See Also:
  Serialized Form

### Field Summary

Fields
`private ResizableDoubleArray` `eDA` Stored data values
`private UnivariateStatistic` `geometricMeanImpl` Geometric mean statistic implementation - can be reset by setter.
`static int` `INFINITE_WINDOW` Represents an infinite window size.
`private UnivariateStatistic` `kurtosisImpl` Kurtosis statistic implementation - can be reset by setter.
`private UnivariateStatistic` `maxImpl` Maximum statistic implementation - can be reset by setter.
`private UnivariateStatistic` `meanImpl` Mean statistic implementation - can be reset by setter.
`private UnivariateStatistic` `minImpl` Minimum statistic implementation - can be reset by setter.
`private UnivariateStatistic` `percentileImpl` Percentile statistic implementation - can be reset by setter.
`private static long` `serialVersionUID` Serialization UID
`private static java.lang.String` `SET_QUANTILE_METHOD_NAME` Name of the setQuantile method.
`private UnivariateStatistic` `skewnessImpl` Skewness statistic implementation - can be reset by setter.
`private UnivariateStatistic` `sumImpl` Sum statistic implementation - can be reset by setter.
`private UnivariateStatistic` `sumsqImpl` Sum of squares statistic implementation - can be reset by setter.
`private UnivariateStatistic` `varianceImpl` Variance statistic implementation - can be reset by setter.
`protected int` `windowSize` hold the window size

### Constructor Summary

Constructors
Constructor and Description
`DescriptiveStatistics()` Construct a DescriptiveStatistics instance with an infinite window
`DescriptiveStatistics(DescriptiveStatistics original)` Copy constructor.
`DescriptiveStatistics(double[] initialDoubleArray)` Construct a DescriptiveStatistics instance with an infinite window and the initial data values in double[] initialDoubleArray.
`DescriptiveStatistics(int window)` Construct a DescriptiveStatistics instance with the specified window

### Method Summary

Methods
`void` `addValue(double v)` Adds the value to the dataset.
`double` `apply(UnivariateStatistic stat)` Apply the given statistic to the data associated with this set of statistics.
`void` `clear()` Resets all statistics and storage
`DescriptiveStatistics` `copy()` Returns a copy of this DescriptiveStatistics instance with the same internal state.
`static void` `copy(DescriptiveStatistics source, DescriptiveStatistics dest)` Copies source to dest.
`double` `getElement(int index)` Returns the element at the specified index
`double` `getGeometricMean()` Returns the geometric mean of the available values
`UnivariateStatistic` `getGeometricMeanImpl()` Returns the currently configured geometric mean implementation.
`double` `getKurtosis()` Returns the Kurtosis of the available values.
`UnivariateStatistic` `getKurtosisImpl()` Returns the currently configured kurtosis implementation.
`double` `getMax()` Returns the maximum of the available values
`UnivariateStatistic` `getMaxImpl()` Returns the currently configured maximum implementation.
`double` `getMean()` Returns the arithmetic mean of the available values
`UnivariateStatistic` `getMeanImpl()` Returns the currently configured mean implementation.
`double` `getMin()` Returns the minimum of the available values
`UnivariateStatistic` `getMinImpl()` Returns the currently configured minimum implementation.
`long` `getN()` Returns the number of available values
`double` `getPercentile(double p)` Returns an estimate for the pth percentile of the stored values.
`UnivariateStatistic` `getPercentileImpl()` Returns the currently configured percentile implementation.
`double` `getPopulationVariance()` Returns the population variance of the available values.
`double` `getSkewness()` Returns the skewness of the available values.
`UnivariateStatistic` `getSkewnessImpl()` Returns the currently configured skewness implementation.
`double[]` `getSortedValues()` Returns the current set of values in an array of double primitives, sorted in ascending order.
`double` `getStandardDeviation()` Returns the standard deviation of the available values.
`double` `getSum()` Returns the sum of the values that have been added to Univariate.
`UnivariateStatistic` `getSumImpl()` Returns the currently configured sum implementation.
`double` `getSumsq()` Returns the sum of the squares of the available values.
`UnivariateStatistic` `getSumsqImpl()` Returns the currently configured sum of squares implementation.
`double[]` `getValues()` Returns the current set of values in an array of double primitives.
`double` `getVariance()` Returns the (sample) variance of the available values.
`UnivariateStatistic` `getVarianceImpl()` Returns the currently configured variance implementation.
`int` `getWindowSize()` Returns the maximum number of values that can be stored in the dataset, or INFINITE_WINDOW (-1) if there is no limit.
`void` `removeMostRecentValue()` Removes the most recent value from the dataset.
`double` `replaceMostRecentValue(double v)` Replaces the most recently stored value with the given value.
`void` `setGeometricMeanImpl(UnivariateStatistic geometricMeanImpl)` Sets the implementation for the gemoetric mean.
`void` `setKurtosisImpl(UnivariateStatistic kurtosisImpl)` Sets the implementation for the kurtosis.
`void` `setMaxImpl(UnivariateStatistic maxImpl)` Sets the implementation for the maximum.
`void` `setMeanImpl(UnivariateStatistic meanImpl)` Sets the implementation for the mean.
`void` `setMinImpl(UnivariateStatistic minImpl)` Sets the implementation for the minimum.
`void` `setPercentileImpl(UnivariateStatistic percentileImpl)` Sets the implementation to be used by `getPercentile(double)`.
`void` `setSkewnessImpl(UnivariateStatistic skewnessImpl)` Sets the implementation for the skewness.
`void` `setSumImpl(UnivariateStatistic sumImpl)` Sets the implementation for the sum.
`void` `setSumsqImpl(UnivariateStatistic sumsqImpl)` Sets the implementation for the sum of squares.
`void` `setVarianceImpl(UnivariateStatistic varianceImpl)` Sets the implementation for the variance.
`void` `setWindowSize(int windowSize)` WindowSize controls the number of values that contribute to the reported statistics.
`java.lang.String` `toString()` Generates a text report displaying univariate statistics from values that have been added.

### Methods inherited from class java.lang.Object

`clone, equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, wait`

### Field Detail

#### INFINITE_WINDOW

    public static final int INFINITE_WINDOW

Represents an infinite window size. When the `getWindowSize()` returns this value, there is no limit to the number of data values that can be stored in the dataset.

See Also:
  Constant Field Values

#### serialVersionUID

    private static final long serialVersionUID

Serialization UID

See Also:
  Constant Field Values

#### SET_QUANTILE_METHOD_NAME

    private static final java.lang.String SET_QUANTILE_METHOD_NAME

Name of the setQuantile method.

See Also:
  Constant Field Values

#### windowSize

    protected int windowSize

hold the window size

#### eDA

    private ResizableDoubleArray eDA

Stored data values

#### meanImpl

    private UnivariateStatistic meanImpl

Mean statistic implementation - can be reset by setter.

#### geometricMeanImpl

    private UnivariateStatistic geometricMeanImpl

Geometric mean statistic implementation - can be reset by setter.

#### kurtosisImpl

    private UnivariateStatistic kurtosisImpl

Kurtosis statistic implementation - can be reset by setter.

#### maxImpl

    private UnivariateStatistic maxImpl

Maximum statistic implementation - can be reset by setter.

#### minImpl

    private UnivariateStatistic minImpl

Minimum statistic implementation - can be reset by setter.

#### percentileImpl

    private UnivariateStatistic percentileImpl

Percentile statistic implementation - can be reset by setter.

#### skewnessImpl

    private UnivariateStatistic skewnessImpl

Skewness statistic implementation - can be reset by setter.

#### varianceImpl

    private UnivariateStatistic varianceImpl

Variance statistic implementation - can be reset by setter.

#### sumsqImpl

    private UnivariateStatistic sumsqImpl

Sum of squares statistic implementation - can be reset by setter.

#### sumImpl

    private UnivariateStatistic sumImpl

Sum statistic implementation - can be reset by setter.

### Constructor Detail

#### DescriptiveStatistics

    public DescriptiveStatistics()

Construct a DescriptiveStatistics instance with an infinite window

#### DescriptiveStatistics

    public DescriptiveStatistics(int window)
                          throws MathIllegalArgumentException

Construct a DescriptiveStatistics instance with the specified window

Parameters:
  `window` - the window size.
Throws:
  `MathIllegalArgumentException` - if window size is less than 1 but not equal to `INFINITE_WINDOW`

#### DescriptiveStatistics

    public DescriptiveStatistics(double[] initialDoubleArray)

Construct a DescriptiveStatistics instance with an infinite window and the initial data values in double[] initialDoubleArray. If initialDoubleArray is null, then this constructor corresponds to DescriptiveStatistics()

Parameters:
  `initialDoubleArray` - the initial double[].

#### DescriptiveStatistics

    public DescriptiveStatistics(DescriptiveStatistics original)
                          throws NullArgumentException

Copy constructor. Construct a new DescriptiveStatistics instance that is a copy of original.

Parameters:
  `original` - DescriptiveStatistics instance to copy
Throws:
  `NullArgumentException` - if original is null

### Method Detail

#### addValue

    public void addValue(double v)

Adds the value to the dataset. If the dataset is at the maximum size (i.e., the number of stored elements equals the currently configured windowSize), the first (oldest) element in the dataset is discarded to make room for the new value.

Parameters:
  `v` - the value to be added

#### removeMostRecentValue

    public void removeMostRecentValue()
                               throws MathIllegalStateException

Removes the most recent value from the dataset.

Throws:
  `MathIllegalStateException` - if there are no elements stored

#### replaceMostRecentValue

    public double replaceMostRecentValue(double v)
                                  throws MathIllegalStateException

Replaces the most recently stored value with the given value. There must be at least one element stored to call this method.

Parameters:
  `v` - the value to replace the most recent stored value
Returns:
  replaced value
Throws:
  `MathIllegalStateException` - if there are no elements stored

#### getMean

    public double getMean()

Returns the arithmetic mean of the available values

Specified by:
  `getMean` in interface `StatisticalSummary`
Returns:
  The mean or Double.NaN if no values have been added.

#### getGeometricMean

    public double getGeometricMean()

Returns the geometric mean of the available values

Returns:
  The geometricMean, Double.NaN if no values have been added, or if the product of the available values is less than or equal to 0.

#### getVariance

    public double getVariance()

Returns the (sample) variance of the available values.

This method returns the bias-corrected sample variance (using `n - 1` in the denominator). Use `getPopulationVariance()` for the non-bias-corrected population variance.

Specified by:
  `getVariance` in interface `StatisticalSummary`
Returns:
  The variance, Double.NaN if no values have been added or 0.0 for a single value set.

#### getPopulationVariance

    public double getPopulationVariance()

Returns the population variance of the available values.

Returns:
  The population variance, Double.NaN if no values have been added, or 0.0 for a single value set.

#### getStandardDeviation

    public double getStandardDeviation()

Returns the standard deviation of the available values.

Specified by:
  `getStandardDeviation` in interface `StatisticalSummary`
Returns:
  The standard deviation, Double.NaN if no values have been added or 0.0 for a single value set.

#### getSkewness

    public double getSkewness()

Returns the skewness of the available values. Skewness is a measure of the asymmetry of a given distribution.

Returns:
  The skewness, Double.NaN if no values have been added or 0.0 for a value set <=2.

#### getKurtosis

    public double getKurtosis()

Returns the Kurtosis of the available values. Kurtosis is a measure of the "peakedness" of a distribution

Returns:
  The kurtosis, Double.NaN if no values have been added, or 0.0 for a value set <=3.

#### getMax

    public double getMax()

Returns the maximum of the available values

Specified by:
  `getMax` in interface `StatisticalSummary`
Returns:
  The max or Double.NaN if no values have been added.

#### getMin

    public double getMin()

Returns the minimum of the available values

Specified by:
  `getMin` in interface `StatisticalSummary`
Returns:
  The min or Double.NaN if no values have been added.

#### getN

    public long getN()

Returns the number of available values

Specified by:
  `getN` in interface `StatisticalSummary`
Returns:
  The number of available values

#### getSum

    public double getSum()

Returns the sum of the values that have been added to Univariate.

Specified by:
  `getSum` in interface `StatisticalSummary`
Returns:
  The sum or Double.NaN if no values have been added

#### getSumsq

    public double getSumsq()

Returns the sum of the squares of the available values.

Returns:
  The sum of the squares or Double.NaN if no values have been added.

#### clear

    public void clear()

Resets all statistics and storage

#### getWindowSize

    public int getWindowSize()

Returns the maximum number of values that can be stored in the dataset, or INFINITE_WINDOW (-1) if there is no limit.

Returns:
  The current window size or -1 if its Infinite.

#### setWindowSize

    public void setWindowSize(int windowSize)
                       throws MathIllegalArgumentException

WindowSize controls the number of values that contribute to the reported statistics. For example, if windowSize is set to 3 and the values {1,2,3,4,5} have been added in that order then the available values are {3,4,5} and all reported statistics will be based on these values. If `windowSize` is decreased as a result of this call and there are more than the new value of elements in the current dataset, values from the front of the array are discarded to reduce the dataset to `windowSize` elements.

Parameters:
  `windowSize` - sets the size of the window.
Throws:
  `MathIllegalArgumentException` - if window size is less than 1 but not equal to `INFINITE_WINDOW`

#### getValues

    public double[] getValues()

Returns the current set of values in an array of double primitives. The order of addition is preserved. The returned array is a fresh copy of the underlying data -- i.e., it is not a reference to the stored data.

Returns:
  returns the current set of numbers in the order in which they were added to this set

#### getSortedValues

    public double[] getSortedValues()

Returns the current set of values in an array of double primitives, sorted in ascending order. The returned array is a fresh copy of the underlying data -- i.e., it is not a reference to the stored data.

Returns:
  returns the current set of numbers sorted in ascending order

#### getElement

    public double getElement(int index)

Returns the element at the specified index

Parameters:
  `index` - The Index of the element
Returns:
  return the element at the specified index

#### getPercentile

    public double getPercentile(double p)
                         throws MathIllegalStateException,
                                MathIllegalArgumentException

Returns an estimate for the pth percentile of the stored values.

The implementation provided here follows the first estimation procedure presented here.

Preconditions:

- `0 < p ≤ 100` (otherwise an `MathIllegalArgumentException` is thrown)
- at least one value must be stored (returns `Double.NaN` otherwise)

Parameters:
  `p` - the requested percentile (scaled from 0 - 100)
Returns:
  An estimate for the pth percentile of the stored data
Throws:
  `MathIllegalStateException` - if percentile implementation has been overridden and the supplied implementation does not support setQuantile
  `MathIllegalArgumentException` - if p is not a valid quantile

#### toString

    public java.lang.String toString()

Generates a text report displaying univariate statistics from values that have been added. Each statistic is displayed on a separate line.

Overrides:
  `toString` in class `java.lang.Object`
Returns:
  String with line feeds displaying statistics

#### apply

    public double apply(UnivariateStatistic stat)

Apply the given statistic to the data associated with this set of statistics.

Parameters:
  `stat` - the statistic to apply
Returns:
  the computed value of the statistic.

#### getMeanImpl

    public UnivariateStatistic getMeanImpl()

Returns the currently configured mean implementation.

Returns:
  the UnivariateStatistic implementing the mean
Since:
  1.2

#### setMeanImpl

    public void setMeanImpl(UnivariateStatistic meanImpl)

Sets the implementation for the mean.

Parameters:
  `meanImpl` - the UnivariateStatistic instance to use for computing the mean
Since:
  1.2

#### getGeometricMeanImpl

    public UnivariateStatistic getGeometricMeanImpl()

Returns the currently configured geometric mean implementation.

Returns:
  the UnivariateStatistic implementing the geometric mean
Since:
  1.2

#### setGeometricMeanImpl

    public void setGeometricMeanImpl(UnivariateStatistic geometricMeanImpl)

Sets the implementation for the gemoetric mean.

Parameters:
  `geometricMeanImpl` - the UnivariateStatistic instance to use for computing the geometric mean
Since:
  1.2

#### getKurtosisImpl

    public UnivariateStatistic getKurtosisImpl()

Returns the currently configured kurtosis implementation.

Returns:
  the UnivariateStatistic implementing the kurtosis
Since:
  1.2

#### setKurtosisImpl

    public void setKurtosisImpl(UnivariateStatistic kurtosisImpl)

Sets the implementation for the kurtosis.

Parameters:
  `kurtosisImpl` - the UnivariateStatistic instance to use for computing the kurtosis
Since:
  1.2

#### getMaxImpl

    public UnivariateStatistic getMaxImpl()

Returns the currently configured maximum implementation.

Returns:
  the UnivariateStatistic implementing the maximum
Since:
  1.2

#### setMaxImpl

    public void setMaxImpl(UnivariateStatistic maxImpl)

Sets the implementation for the maximum.

Parameters:
  `maxImpl` - the UnivariateStatistic instance to use for computing the maximum
Since:
  1.2

#### getMinImpl

    public UnivariateStatistic getMinImpl()

Returns the currently configured minimum implementation.

Returns:
  the UnivariateStatistic implementing the minimum
Since:
  1.2

#### setMinImpl

    public void setMinImpl(UnivariateStatistic minImpl)

Sets the implementation for the minimum.

Parameters:
  `minImpl` - the UnivariateStatistic instance to use for computing the minimum
Since:
  1.2

#### getPercentileImpl

    public UnivariateStatistic getPercentileImpl()

Returns the currently configured percentile implementation.

Returns:
  the UnivariateStatistic implementing the percentile
Since:
  1.2

#### setPercentileImpl

    public void setPercentileImpl(UnivariateStatistic percentileImpl)
                           throws MathIllegalArgumentException

Sets the implementation to be used by `getPercentile(double)`. The supplied `UnivariateStatistic` must provide a `setQuantile(double)` method; otherwise `IllegalArgumentException` is thrown.

Parameters:
  `percentileImpl` - the percentileImpl to set
Throws:
  `MathIllegalArgumentException` - if the supplied implementation does not provide a `setQuantile` method
Since:
  1.2

#### getSkewnessImpl

    public UnivariateStatistic getSkewnessImpl()

Returns the currently configured skewness implementation.

Returns:
  the UnivariateStatistic implementing the skewness
Since:
  1.2

#### setSkewnessImpl

    public void setSkewnessImpl(UnivariateStatistic skewnessImpl)

Sets the implementation for the skewness.

Parameters:
  `skewnessImpl` - the UnivariateStatistic instance to use for computing the skewness
Since:
  1.2

#### getVarianceImpl

    public UnivariateStatistic getVarianceImpl()

Returns the currently configured variance implementation.

Returns:
  the UnivariateStatistic implementing the variance
Since:
  1.2

#### setVarianceImpl

    public void setVarianceImpl(UnivariateStatistic varianceImpl)

Sets the implementation for the variance.

Parameters:
  `varianceImpl` - the UnivariateStatistic instance to use for computing the variance
Since:
  1.2

#### getSumsqImpl

    public UnivariateStatistic getSumsqImpl()

Returns the currently configured sum of squares implementation.

Returns:
  the UnivariateStatistic implementing the sum of squares
Since:
  1.2

#### setSumsqImpl

    public void setSumsqImpl(UnivariateStatistic sumsqImpl)

Sets the implementation for the sum of squares.

Parameters:
  `sumsqImpl` - the UnivariateStatistic instance to use for computing the sum of squares
Since:
  1.2

#### getSumImpl

    public UnivariateStatistic getSumImpl()

Returns the currently configured sum implementation.

Returns:
  the UnivariateStatistic implementing the sum
Since:
  1.2

#### setSumImpl

    public void setSumImpl(UnivariateStatistic sumImpl)

Sets the implementation for the sum.

Parameters:
  `sumImpl` - the UnivariateStatistic instance to use for computing the sum
Since:
  1.2

#### copy

    public DescriptiveStatistics copy()

Returns a copy of this DescriptiveStatistics instance with the same internal state.

Returns:
  a copy of this

#### copy

    public static void copy(DescriptiveStatistics source,
            DescriptiveStatistics dest)
                     throws NullArgumentException

Copies source to dest.

Neither source nor dest can be null.

Parameters:
  `source` - DescriptiveStatistics to copy
  `dest` - DescriptiveStatistics to copy to
Throws:
  `NullArgumentException` - if either source or dest is null