Class EnumeratedDistribution<T>

java.lang.Object
org.apache.commons.math3.distribution.EnumeratedDistribution<T>
Type Parameters:
T - type of the elements in the sample space.
All Implemented Interfaces:
Serializable

public class EnumeratedDistribution<T> extends Object implements Serializable

A generic implementation of a discrete probability distribution (Wikipedia) over a finite sample space, based on an enumerated list of <value, probability> pairs. Input probabilities must all be non-negative, but zero values are allowed and their sum does not have to equal one. Constructors will normalize input probabilities to make them sum to one.

The list of invalid input: '<'value, probability> pairs does not, strictly speaking, have to be a function and it can contain null values. The pmf created by the constructor will combine probabilities of equal values and will treat null values as equal. For example, if the list of pairs <"dog", 0.2>, <null, 0.1>, <"pig", 0.2>, <"dog", 0.1>, <null, 0.4> is provided to the constructor, the resulting pmf will assign mass of 0.5 to null, 0.3 to "dog" and 0.2 to null.

Since:
3.2
See Also:
  • Field Summary

    Fields
    Modifier and Type
    Field
    Description
    private final double[]
    Cumulative probabilities, cached to speed up sampling.
    private final double[]
    Probabilities of respective random variable values.
    protected final RandomGenerator
    RNG instance used to generate samples from the distribution.
    private static final long
    Serializable UID.
    private final List<T>
    List of random variable values.
  • Constructor Summary

    Constructors
    Constructor
    Description
    Create an enumerated distribution using the given probability mass function enumeration.
    Create an enumerated distribution using the given random number generator and probability mass function enumeration.
  • Method Summary

    Modifier and Type
    Method
    Description
    Return the probability mass function as a list of invalid input: '<'value, probability> pairs.
    (package private) double
    For a random variable X whose values are distributed according to this distribution, this method returns P(X = x).
    void
    Reseed the random generator used to generate samples.
    Generate a random value sampled from this distribution.
    sample(int sampleSize)
    Generate a random sample from the distribution.
    T[]
    sample(int sampleSize, T[] array)
    Generate a random sample from the distribution.

    Methods inherited from class java.lang.Object

    clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait
  • Field Details

    • serialVersionUID

      private static final long serialVersionUID
      Serializable UID.
      See Also:
    • random

      protected final RandomGenerator random
      RNG instance used to generate samples from the distribution.
    • singletons

      private final List<T> singletons
      List of random variable values.
    • probabilities

      private final double[] probabilities
      Probabilities of respective random variable values. For i = 0, ..., singletons.size() - 1, probability[i] is the probability that a random variable following this distribution takes the value singletons[i].
    • cumulativeProbabilities

      private final double[] cumulativeProbabilities
      Cumulative probabilities, cached to speed up sampling.
  • Constructor Details

  • Method Details

    • reseedRandomGenerator

      public void reseedRandomGenerator(long seed)
      Reseed the random generator used to generate samples.
      Parameters:
      seed - the new seed
    • probability

      double probability(T 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.

      Note that if x1 and x2 satisfy x1.equals(x2), or both are null, then probability(x1) = probability(x2).

      Parameters:
      x - the point at which the PMF is evaluated
      Returns:
      the value of the probability mass function at x
    • getPmf

      public List<Pair<T,Double>> getPmf()

      Return the probability mass function as a list of invalid input: '<'value, probability> pairs.

      Note that if duplicate and / or null values were provided to the constructor when creating this EnumeratedDistribution, the returned list will contain these values. If duplicates values exist, what is returned will not represent a pmf (i.e., it is up to the caller to consolidate duplicate mass points).

      Returns:
      the probability mass function.
    • sample

      public T sample()
      Generate a random value sampled from this distribution.
      Returns:
      a random value.
    • sample

      public Object[] sample(int sampleSize) throws NotStrictlyPositiveException
      Generate a random sample from the distribution.
      Parameters:
      sampleSize - the number of random values to generate.
      Returns:
      an array representing the random sample.
      Throws:
      NotStrictlyPositiveException - if sampleSize is not positive.
    • sample

      public T[] sample(int sampleSize, T[] array) throws NotStrictlyPositiveException
      Generate a random sample from the distribution.

      If the requested samples fit in the specified array, it is returned therein. Otherwise, a new array is allocated with the runtime type of the specified array and the size of this collection.

      Parameters:
      sampleSize - the number of random values to generate.
      array - the array to populate.
      Returns:
      an array representing the random sample.
      Throws:
      NotStrictlyPositiveException - if sampleSize is not positive.
      NullArgumentException - if array is null