org.apache.commons.math3.random

## Class EmpiricalDistribution

- java.lang.Object
- - org.apache.commons.math3.distribution.AbstractRealDistribution
  - - org.apache.commons.math3.random.EmpiricalDistribution

All Implemented Interfaces:
  Serializable, RealDistribution

    public class EmpiricalDistribution
    extends AbstractRealDistribution

Represents an empirical probability distribution -- a probability distribution derived from observed data without making any assumptions about the functional form of the population distribution that the data come from.

An `EmpiricalDistribution` maintains data structures, called distribution digests, that describe empirical distributions and support the following operations:

- loading the distribution from a file of observed data values
- dividing the input data into "bin ranges" and reporting bin frequency counts (data for histogram)
- reporting univariate statistics describing the full set of data values as well as the observations within each bin
- generating random values from the distribution

Applications can use `EmpiricalDistribution` to build grouped frequency histograms representing the input data or to generate random values "like" those in the input file -- i.e., the values generated will follow the distribution of the values in the file.

The implementation uses what amounts to the Variable Kernel Method with Gaussian smoothing:

Digesting the input file

1. Pass the file once to compute min and max.
2. Divide the range from min-max into `binCount` "bins."
3. Pass the data file again, computing bin counts and univariate statistics (mean, std dev.) for each of the bins
4. Divide the interval (0,1) into subintervals associated with the bins, with the length of a bin's subinterval proportional to its count.

Generating random values from the distribution

1. Generate a uniformly distributed value in (0,1)
2. Select the subinterval to which the value belongs.
3. Generate a random Gaussian value with mean = mean of the associated bin and std dev = std dev of associated bin.

EmpiricalDistribution implements the `RealDistribution` interface as follows. Given x within the range of values in the dataset, let B be the bin containing x and let K be the within-bin kernel for B. Let P(B-) be the sum of the probabilities of the bins below B and let K(B) be the mass of B under K (i.e., the integral of the kernel density over B). Then set P(X < x) = P(B-) + P(B) * K(x) / K(B) where K(x) is the kernel distribution evaluated at x. This results in a cdf that matches the grouped frequency distribution at the bin endpoints and interpolates within bins using within-bin kernels.

USAGE NOTES:

- The `binCount` is set by default to 1000. A good rule of thumb is to set the bin count to approximately the length of the input file divided by 10.
- The input file must be a plain text file containing one valid numeric entry per line.

Version:
  $Id: EmpiricalDistribution.java 1422350 2012-12-15 20:47:47Z psteitz $
See Also:
  Serialized Form

### Nested Class Summary

Nested Classes
`private class` `EmpiricalDistribution.ArrayDataAdapter` `DataAdapter` for data provided as array of doubles.
`private class` `EmpiricalDistribution.DataAdapter` Provides methods for computing `sampleStats` and `beanStats` abstracting the source of data.
`private class` `EmpiricalDistribution.StreamDataAdapter` `DataAdapter` for data provided through some input stream

### Field Summary

Fields
`private int` `binCount` number of bins
`private List<SummaryStatistics>` `binStats` List of SummaryStatistics objects characterizing the bins
`static int` `DEFAULT_BIN_COUNT` Default bin count
`private double` `delta` Grid size
`private static String` `FILE_CHARSET` Character set for file input
`private boolean` `loaded` is the distribution loaded?
`private double` `max` Max loaded value
`private double` `min` Min loaded value
`private RandomDataGenerator` `randomData` RandomDataGenerator instance to use in repeated calls to getNext()
`private SummaryStatistics` `sampleStats` Sample statistics
`private static long` `serialVersionUID` Serializable version identifier
`private double[]` `upperBounds` upper bounds of subintervals in (0,1) "belonging" to the bins

### Fields inherited from class org.apache.commons.math3.distribution.AbstractRealDistribution

`random, SOLVER_DEFAULT_ABSOLUTE_ACCURACY`

### Constructor Summary

Constructors
`` `EmpiricalDistribution()` Creates a new EmpiricalDistribution with the default bin count.
`` `EmpiricalDistribution(int binCount)` Creates a new EmpiricalDistribution with the specified bin count.
`private` `EmpiricalDistribution(int binCount, RandomDataGenerator randomData)` Private constructor to allow lazy initialisation of the RNG contained in the `randomData` instance variable.
`` `EmpiricalDistribution(int binCount, RandomDataImpl randomData)` Deprecated. As of 3.1. Please use `EmpiricalDistribution(int,RandomGenerator)` instead.
`` `EmpiricalDistribution(int binCount, RandomGenerator generator)` Creates a new EmpiricalDistribution with the specified bin count using the provided `RandomGenerator` as the source of random data.
`` `EmpiricalDistribution(RandomDataImpl randomData)` Deprecated. As of 3.1. Please use `EmpiricalDistribution(RandomGenerator)` instead.
`` `EmpiricalDistribution(RandomGenerator generator)` Creates a new EmpiricalDistribution with default bin count using the provided `RandomGenerator` as the source of random data.

### Method Summary

Methods
`private double` `cumBinP(int binIndex)` The combined probability of the bins up to and including binIndex.
`double` `cumulativeProbability(double x)` For a random variable `X` whose values are distributed according to this distribution, this method returns `P(X <= x)`.
`double` `density(double x)` Returns the probability density function (PDF) of this distribution evaluated at the specified point `x`.
`private void` `fillBinStats(EmpiricalDistribution.DataAdapter da)` Fills binStats array (second pass through data file).
`private int` `findBin(double value)` Returns the index of the bin to which the given value belongs
`int` `getBinCount()` Returns the number of bins.
`List<SummaryStatistics>` `getBinStats()` Returns a List of `SummaryStatistics` instances containing statistics describing the values in each of the bins.
`double[]` `getGeneratorUpperBounds()` Returns a fresh copy of the array of upper bounds of the subintervals of [0,1] used in generating data from the empirical distribution.
`private RealDistribution` `getKernel(SummaryStatistics bStats)` The within-bin smoothing kernel.
`double` `getNextValue()` Generates a random value from this distribution.
`double` `getNumericalMean()` Use this method to get the numerical value of the mean of this distribution.
`double` `getNumericalVariance()` Use this method to get the numerical value of the variance of this distribution.
`StatisticalSummary` `getSampleStats()` Returns a `StatisticalSummary` describing this distribution.
`double` `getSupportLowerBound()` Access the lower bound of the support.
`double` `getSupportUpperBound()` Access the upper bound of the support.
`double[]` `getUpperBounds()` Returns a fresh copy of the array of upper bounds for the bins.
`double` `inverseCumulativeProbability(double p)` Computes the quantile function of this distribution.
`boolean` `isLoaded()` Property indicating whether or not the distribution has been loaded.
`boolean` `isSupportConnected()` Use this method to get information about whether the support is connected, i.e.
`boolean` `isSupportLowerBoundInclusive()` Whether or not the lower bound of support is in the domain of the density function.
`boolean` `isSupportUpperBoundInclusive()` Whether or not the upper bound of support is in the domain of the density function.
`private RealDistribution` `k(double x)` The within-bin kernel of the bin that x belongs to.
`private double` `kB(int i)` Mass of bin i under the within-bin kernel of the bin.
`void` `load(double[] in)` Computes the empirical distribution from the provided array of numbers.
`void` `load(File file)` Computes the empirical distribution from the input file.
`void` `load(URL url)` Computes the empirical distribution using data read from a URL.
`private double` `pB(int i)` The probability of bin i.
`private double` `pBminus(int i)` The combined probability of the bins up to but not including bin i.
`double` `probability(double x)` For a random variable `X` whose values are distributed according to this distribution, this method returns `P(X = x)`.
`void` `reSeed(long seed)` Reseeds the random number generator used by `getNextValue()`.
`void` `reseedRandomGenerator(long seed)` Reseed the random generator used to generate samples.
`double` `sample()` Generate a random value sampled from this distribution.

### Methods inherited from class org.apache.commons.math3.distribution.AbstractRealDistribution

`cumulativeProbability, getSolverAbsoluteAccuracy, probability, sample`

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

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

### Field Detail

#### DEFAULT_BIN_COUNT

    public static final int DEFAULT_BIN_COUNT

Default bin count

See Also:
  Constant Field Values

#### FILE_CHARSET

    private static final String FILE_CHARSET

Character set for file input

See Also:
  Constant Field Values

#### serialVersionUID

    private static final long serialVersionUID

Serializable version identifier

See Also:
  Constant Field Values

#### binStats

    private final List<SummaryStatistics> binStats

List of SummaryStatistics objects characterizing the bins

#### sampleStats

    private SummaryStatistics sampleStats

Sample statistics

#### max

    private double max

Max loaded value

#### min

    private double min

Min loaded value

#### delta

    private double delta

Grid size

#### binCount

    private final int binCount

number of bins

#### loaded

    private boolean loaded

is the distribution loaded?

#### upperBounds

    private double[] upperBounds

upper bounds of subintervals in (0,1) "belonging" to the bins

#### randomData

    private final RandomDataGenerator randomData

RandomDataGenerator instance to use in repeated calls to getNext()

### Constructor Detail

#### EmpiricalDistribution

    public EmpiricalDistribution()

Creates a new EmpiricalDistribution with the default bin count.

#### EmpiricalDistribution

    public EmpiricalDistribution(int binCount)

Creates a new EmpiricalDistribution with the specified bin count.

Parameters:
  `binCount` - number of bins

#### EmpiricalDistribution

    public EmpiricalDistribution(int binCount,
                         RandomGenerator generator)

Creates a new EmpiricalDistribution with the specified bin count using the provided `RandomGenerator` as the source of random data.

Parameters:
  `binCount` - number of bins
  `generator` - random data generator (may be null, resulting in default JDK generator)
Since:
  3.0

#### EmpiricalDistribution

    public EmpiricalDistribution(RandomGenerator generator)

Creates a new EmpiricalDistribution with default bin count using the provided `RandomGenerator` as the source of random data.

Parameters:
  `generator` - random data generator (may be null, resulting in default JDK generator)
Since:
  3.0

#### EmpiricalDistribution

    @Deprecated
    public EmpiricalDistribution(int binCount,
                                    RandomDataImpl randomData)

Deprecated. As of 3.1. Please use `EmpiricalDistribution(int,RandomGenerator)` instead.
Creates a new EmpiricalDistribution with the specified bin count using the provided `RandomDataImpl` instance as the source of random data.

Parameters:
  `binCount` - number of bins
  `randomData` - random data generator (may be null, resulting in default JDK generator)
Since:
  3.0

#### EmpiricalDistribution

    @Deprecated
    public EmpiricalDistribution(RandomDataImpl randomData)

Deprecated. As of 3.1. Please use `EmpiricalDistribution(RandomGenerator)` instead.
Creates a new EmpiricalDistribution with default bin count using the provided `RandomDataImpl` as the source of random data.

Parameters:
  `randomData` - random data generator (may be null, resulting in default JDK generator)
Since:
  3.0

#### EmpiricalDistribution

    private EmpiricalDistribution(int binCount,
                         RandomDataGenerator randomData)

Private constructor to allow lazy initialisation of the RNG contained in the `randomData` instance variable.

Parameters:
  `binCount` - number of bins
  `randomData` - Random data generator.

### Method Detail

#### load

    public void load(double[] in)
              throws NullArgumentException

Computes the empirical distribution from the provided array of numbers.

Parameters:
  `in` - the input data array
Throws:
  `NullArgumentException` - if in is null

#### load

    public void load(URL url)
              throws IOException,
                     NullArgumentException,
                     ZeroException

Computes the empirical distribution using data read from a URL.

The input file must be an ASCII text file containing one valid numeric entry per line.

Parameters:
  `url` - url of the input file
Throws:
  `IOException` - if an IO error occurs
  `NullArgumentException` - if url is null
  `ZeroException` - if URL contains no data

#### load

    public void load(File file)
              throws IOException,
                     NullArgumentException

Computes the empirical distribution from the input file.

The input file must be an ASCII text file containing one valid numeric entry per line.

Parameters:
  `file` - the input file
Throws:
  `IOException` - if an IO error occurs
  `NullArgumentException` - if file is null

#### fillBinStats

    private void fillBinStats(EmpiricalDistribution.DataAdapter da)
                       throws IOException

Fills binStats array (second pass through data file).

Parameters:
  `da` - object providing access to the data
Throws:
  `IOException` - if an IO error occurs

#### findBin

    private int findBin(double value)

Returns the index of the bin to which the given value belongs

Parameters:
  `value` - the value whose bin we are trying to find
Returns:
  the index of the bin containing the value

#### getNextValue

    public double getNextValue()
                        throws MathIllegalStateException

Generates a random value from this distribution. Preconditions:

- the distribution must be loaded before invoking this method

Returns:
  the random value.
Throws:
  `MathIllegalStateException` - if the distribution has not been loaded

#### getSampleStats

    public StatisticalSummary getSampleStats()

Returns a `StatisticalSummary` describing this distribution. Preconditions:

- the distribution must be loaded before invoking this method

Returns:
  the sample statistics
Throws:
  `IllegalStateException` - if the distribution has not been loaded

#### getBinCount

    public int getBinCount()

Returns the number of bins.

Returns:
  the number of bins.

#### getBinStats

    public List<SummaryStatistics> getBinStats()

Returns a List of `SummaryStatistics` instances containing statistics describing the values in each of the bins. The list is indexed on the bin number.

Returns:
  List of bin statistics.

#### getUpperBounds

    public double[] getUpperBounds()

Returns a fresh copy of the array of upper bounds for the bins. Bins are:
[min,upperBounds[0]],(upperBounds[0],upperBounds[1]],..., (upperBounds[binCount-2], upperBounds[binCount-1] = max].

Note: In versions 1.0-2.0 of commons-math, this method incorrectly returned the array of probability generator upper bounds now returned by `getGeneratorUpperBounds()`.

Returns:
  array of bin upper bounds
Since:
  2.1

#### getGeneratorUpperBounds

    public double[] getGeneratorUpperBounds()

Returns a fresh copy of the array of upper bounds of the subintervals of [0,1] used in generating data from the empirical distribution. Subintervals correspond to bins with lengths proportional to bin counts.

In versions 1.0-2.0 of commons-math, this array was (incorrectly) returned by `getUpperBounds()`.

Returns:
  array of upper bounds of subintervals used in data generation
Since:
  2.1

#### isLoaded

    public boolean isLoaded()

Property indicating whether or not the distribution has been loaded.

Returns:
  true if the distribution has been loaded

#### reSeed

    public void reSeed(long seed)

Reseeds the random number generator used by `getNextValue()`.

Parameters:
  `seed` - random generator seed
Since:
  3.0

#### probability

    public double probability(double x)

For a random variable `X` whose values are distributed according to this distribution, this method returns `P(X = x)`. In other words, this method represents the probability mass function (PMF) for the distribution.

Specified by:
  `probability` in interface `RealDistribution`
Overrides:
  `probability` in class `AbstractRealDistribution`
Parameters:
  `x` - the point at which the PMF is evaluated
Returns:
  zero.
Since:
  3.1

#### density

    public double density(double x)

Returns the probability density function (PDF) of this distribution evaluated at the specified point `x`. In general, the PDF is the derivative of the `CDF`. If the derivative does not exist at `x`, then an appropriate replacement should be returned, e.g. `Double.POSITIVE_INFINITY`, `Double.NaN`, or the limit inferior or limit superior of the difference quotient.

Returns the kernel density normalized so that its integral over each bin equals the bin mass.

Algorithm description:

1. Find the bin B that x belongs to.
2. Compute K(B) = the mass of B with respect to the within-bin kernel (i.e., the integral of the kernel density over B).
3. Return k(x) * P(B) / K(B), where k is the within-bin kernel density and P(B) is the mass of B.

Parameters:
  `x` - the point at which the PDF is evaluated
Returns:
  the value of the probability density function at point `x`
Since:
  3.1

#### cumulativeProbability

    public double cumulativeProbability(double x)

For a random variable `X` whose values are distributed according to this distribution, this method returns `P(X <= x)`. In other words, this method represents the (cumulative) distribution function (CDF) for this distribution.

Algorithm description:

1. Find the bin B that x belongs to.
2. Compute P(B) = the mass of B and P(B-) = the combined mass of the bins below B.
3. Compute K(B) = the probability mass of B with respect to the within-bin kernel and K(B-) = the kernel distribution evaluated at the lower endpoint of B
4. Return P(B-) + P(B) * [K(x) - K(B-)] / K(B) where K(x) is the within-bin kernel distribution function evaluated at x.

Parameters:
  `x` - the point at which the CDF is evaluated
Returns:
  the probability that a random variable with this distribution takes a value less than or equal to `x`
Since:
  3.1

#### inverseCumulativeProbability

    public double inverseCumulativeProbability(double p)
                                        throws OutOfRangeException

Computes the quantile function of this distribution. For a random variable `X` distributed according to this distribution, the returned value is

- `inf{x in R | P(X<=x) >= p}` for `0 < p <= 1`,
- `inf{x in R | P(X<=x) > 0}` for `p = 0`.

The default implementation returns

- `RealDistribution.getSupportLowerBound()` for `p = 0`,
- `RealDistribution.getSupportUpperBound()` for `p = 1`.

Algorithm description:

1. Find the smallest i such that the sum of the masses of the bins through i is at least p.
2. Let K be the within-bin kernel distribution for bin i. Let K(B) be the mass of B under K.
   Let K(B-) be K evaluated at the lower endpoint of B (the combined mass of the bins below B under K).
   Let P(B) be the probability of bin i.
   Let P(B-) be the sum of the bin masses below bin i.
   Let pCrit = p - P(B-)
3. Return the inverse of K evaluated at
   K(B-) + pCrit * K(B) / P(B)

Specified by:
  `inverseCumulativeProbability` in interface `RealDistribution`
Overrides:
  `inverseCumulativeProbability` in class `AbstractRealDistribution`
Parameters:
  `p` - the cumulative probability
Returns:
  the smallest `p`-quantile of this distribution (largest 0-quantile for `p = 0`)
Throws:
  `OutOfRangeException` - if `p < 0` or `p > 1`
Since:
  3.1

#### getNumericalMean

    public double getNumericalMean()

Use this method to get the numerical value of the mean of this distribution.

Returns:
  the mean or `Double.NaN` if it is not defined
Since:
  3.1

#### getNumericalVariance

    public double getNumericalVariance()

Use this method to get the numerical value of the variance of this distribution.

Returns:
  the variance (possibly `Double.POSITIVE_INFINITY` as for certain cases in `TDistribution`) or `Double.NaN` if it is not defined
Since:
  3.1

#### getSupportLowerBound

    public double getSupportLowerBound()

Access the lower bound of the support. This method must return the same value as `inverseCumulativeProbability(0)`. In other words, this method must return

`inf {x in R | P(X <= x) > 0}`.

Returns:
  lower bound of the support (might be `Double.NEGATIVE_INFINITY`)
Since:
  3.1

#### getSupportUpperBound

    public double getSupportUpperBound()

Access the upper bound of the support. This method must return the same value as `inverseCumulativeProbability(1)`. In other words, this method must return

`inf {x in R | P(X <= x) = 1}`.

Returns:
  upper bound of the support (might be `Double.POSITIVE_INFINITY`)
Since:
  3.1

#### isSupportLowerBoundInclusive

    public boolean isSupportLowerBoundInclusive()

Whether or not the lower bound of support is in the domain of the density function. Returns true iff `getSupporLowerBound()` is finite and `density(getSupportLowerBound())` returns a non-NaN, non-infinite value.

Returns:
  true if the lower bound of support is finite and the density function returns a non-NaN, non-infinite value there
Since:
  3.1

#### isSupportUpperBoundInclusive

    public boolean isSupportUpperBoundInclusive()

Whether or not the upper bound of support is in the domain of the density function. Returns true iff `getSupportUpperBound()` is finite and `density(getSupportUpperBound())` returns a non-NaN, non-infinite value.

Returns:
  true if the upper bound of support is finite and the density function returns a non-NaN, non-infinite value there
Since:
  3.1

#### isSupportConnected

    public boolean isSupportConnected()

Use this method to get information about whether the support is connected, i.e. whether all values between the lower and upper bound of the support are included in the support.

Returns:
  whether the support is connected or not
Since:
  3.1

#### sample

    public double sample()

Generate a random value sampled from this distribution. The default implementation uses the inversion method.

Specified by:
  `sample` in interface `RealDistribution`
Overrides:
  `sample` in class `AbstractRealDistribution`
Returns:
  a random value.
Since:
  3.1

#### reseedRandomGenerator

    public void reseedRandomGenerator(long seed)

Reseed the random generator used to generate samples.

Specified by:
  `reseedRandomGenerator` in interface `RealDistribution`
Overrides:
  `reseedRandomGenerator` in class `AbstractRealDistribution`
Parameters:
  `seed` - the new seed
Since:
  3.1

#### pB

    private double pB(int i)

The probability of bin i.

Parameters:
  `i` - the index of the bin
Returns:
  the probability that selection begins in bin i

#### pBminus

    private double pBminus(int i)

The combined probability of the bins up to but not including bin i.

Parameters:
  `i` - the index of the bin
Returns:
  the probability that selection begins in a bin below bin i.

#### kB

    private double kB(int i)

Mass of bin i under the within-bin kernel of the bin.

Parameters:
  `i` - index of the bin
Returns:
  the difference in the within-bin kernel cdf between the upper and lower endpoints of bin i

#### k

    private RealDistribution k(double x)

The within-bin kernel of the bin that x belongs to.

Parameters:
  `x` - the value to locate within a bin
Returns:
  the within-bin kernel of the bin containing x

#### cumBinP

    private double cumBinP(int binIndex)

The combined probability of the bins up to and including binIndex.

Parameters:
  `binIndex` - maximum bin index
Returns:
  sum of the probabilities of bins through binIndex

#### getKernel

    private RealDistribution getKernel(SummaryStatistics bStats)

The within-bin smoothing kernel.

Parameters:
  `bStats` - summary statistics for the bin
Returns:
  within-bin kernel parameterized by bStats