---
name: "mlpack_distribution_DiscreteDistribution"
section: "3"
platform: "linux"
package: "mlpack-doc"
version: "1.0.10-1"
release: "Debian 8 (Jessie)"
platforms: ["linux"]
url: "https://new.carta.tech/mlpack_distribution_DiscreteDistribution"
---

# mlpack\_distribution\_DiscreteDistribution(3)

A discrete distribution where the only observations are discrete observations.

## NAME

mlpack::distribution::DiscreteDistribution -

A discrete distribution where the only observations are discrete observations.

## SYNOPSIS

### Public Member Functions

**DiscreteDistribution** ()\
 *Default constructor, which creates a distribution that has no observations.*  **DiscreteDistribution** (const size\_t numObservations)\
 *Define the discrete distribution as having numObservations possible observations.*  **DiscreteDistribution** (const arma::vec &**probabilities**)\
 *Define the discrete distribution as having the given probabilities for each observation.*  size\_t **Dimensionality** () const \
 *Get the dimensionality of the distribution.*  void **Estimate** (const arma::mat &observations)\
 *Estimate the probability distribution directly from the given observations.*  void **Estimate** (const arma::mat &observations, const arma::vec &**probabilities**)\
 *Estimate the probability distribution from the given observations, taking into account the probability of each observation actually being from this distribution.*  const arma::vec & **Probabilities** () const \
 *Return the vector of probabilities.*  arma::vec & **Probabilities** ()\
 *Modify the vector of probabilities.*  double **Probability** (const arma::vec &observation) const \
 *Return the probability of the given observation.*  arma::vec **Random** () const \
 *Return a randomly generated observation (one-dimensional vector; one observation) according to the probability distribution defined by this object.*  std::string **ToString** () const \

### Private Attributes

arma::vec **probabilities**\

## Detailed Description

A discrete distribution where the only observations are discrete observations.

This is useful (for example) with discrete Hidden Markov Models, where observations are non-negative integers representing specific emissions.

No bounds checking is performed for observations, so if an invalid observation is passed (i.e. observation \> numObservations), a crash will probably occur.

This distribution only supports one-dimensional observations, so when passing an arma::vec as an observation, it should only have one dimension (vec.n\_rows == 1). Any additional dimensions will simply be ignored.

**Note:**

This class, like every other class in MLPACK, uses arma::vec to represent observations. While a discrete distribution only has positive integers (size\_t) as observations, these can be converted to doubles (which is what arma::vec holds). This distribution internally converts those doubles back into size\_t before comparisons.

Definition at line 53 of file discrete\_distribution.hpp.

## Constructor & Destructor Documentation

### mlpack::distribution::DiscreteDistribution::DiscreteDistribution ()` [inline]`

Default constructor, which creates a distribution that has no observations.

Definition at line 59 of file discrete\_distribution.hpp.

### mlpack::distribution::DiscreteDistribution::DiscreteDistribution (const size\_tnumObservations)` [inline]`

Define the discrete distribution as having numObservations possible observations. The probability in each state will be set to (1 / numObservations).

**Parameters:**

*numObservations* Number of possible observations this distribution can have.

Definition at line 69 of file discrete\_distribution.hpp.

### mlpack::distribution::DiscreteDistribution::DiscreteDistribution (const arma::vec &probabilities)` [inline]`

Define the discrete distribution as having the given probabilities for each observation.

**Parameters:**

*probabilities* Probabilities of each possible observation.

Definition at line 79 of file discrete\_distribution.hpp.

## Member Function Documentation

### size\_t mlpack::distribution::DiscreteDistribution::Dimensionality () const` [inline]`

Get the dimensionality of the distribution.

Definition at line 95 of file discrete\_distribution.hpp.

### void mlpack::distribution::DiscreteDistribution::Estimate (const arma::mat &observations)

Estimate the probability distribution directly from the given observations. If any of the observations is greater than numObservations, a crash is likely to occur.

**Parameters:**

*observations* List of observations.

### void mlpack::distribution::DiscreteDistribution::Estimate (const arma::mat &observations, const arma::vec &probabilities)

Estimate the probability distribution from the given observations, taking into account the probability of each observation actually being from this distribution.

**Parameters:**

*observations* List of observations. \
 *probabilities* List of probabilities that each observation is actually from this distribution.

### const arma::vec& mlpack::distribution::DiscreteDistribution::Probabilities () const` [inline]`

Return the vector of probabilities.

Definition at line 153 of file discrete\_distribution.hpp.

References probabilities.

### arma::vec& mlpack::distribution::DiscreteDistribution::Probabilities ()` [inline]`

Modify the vector of probabilities.

Definition at line 155 of file discrete\_distribution.hpp.

References probabilities.

### double mlpack::distribution::DiscreteDistribution::Probability (const arma::vec &observation) const` [inline]`

Return the probability of the given observation. If the observation is greater than the number of possible observations, then a crash will probably occur -- bounds checking is not performed.

**Parameters:**

*observation* Observation to return the probability of.

**Returns:**

Probability of the given observation.

Definition at line 105 of file discrete\_distribution.hpp.

References mlpack::Log::Debug, and probabilities.

### arma::vec mlpack::distribution::DiscreteDistribution::Random () const

Return a randomly generated observation (one-dimensional vector; one observation) according to the probability distribution defined by this object.

**Returns:**

Random observation.

### std::string mlpack::distribution::DiscreteDistribution::ToString () const

## Member Data Documentation

### arma::vec mlpack::distribution::DiscreteDistribution::probabilities` [private]`

Definition at line 163 of file discrete\_distribution.hpp.

Referenced by Probabilities(), and Probability().

## Author

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