discrete_distribution Class
The latest version of this topic can be found at discrete_distribution Class.
Generates a discrete integer distribution that has uniform-width intervals with uniform probability in each interval.
Syntax
class discrete_distribution
{
public: // types
typedef IntType result_type;
struct param_type; // constructor and reset functions
discrete_distribution();
template <class InputIterator>
discrete_distribution(InputIterator firstW, InputIterator lastW);
discrete_distribution(initializer_list<double>
weightlist);
template <class UnaryOperation>
discrete_distribution(size_t count, double xmin, double xmax, UnaryOperation funcweight);
explicit discrete_distribution(const param_type& parm);
void reset();
// generating functions
template <class URNG>
result_type operator()(URNG& gen);
template <class URNG>
result_type operator()(URNG& gen, const param_type& parm);
// property functions
vector<double>
probabilities() const;
param_type param() const;
void param(const param_type& parm);
result_type min() const;
result_type max() const;
};
Parameters
IntType
The integer result type, defaults to int. For possible types, see <random>.
Remarks
This sampling distribution has uniform-width intervals with uniform probability in each interval. For information about other sampling distributions, see piecewise_linear_distribution Class and piecewise_constant_distribution Class.
The following table links to articles about individual members:
| discrete_distribution::discrete_distribution | discrete_distribution::param |
discrete_distribution::operator() |
discrete_distribution::param_type |
The property function vector<double> probabilities() returns the individual probabilities for each integer generated.
For more information about distribution classes and their members, see <random>.
Example
// compile with: /EHsc /W4
#include <random>
#include <iostream>
#include <iomanip>
#include <string>
#include <map>
using namespace std;
void test(const int s) {
// uncomment to use a non-deterministic generator
// random_device rd;
// mt19937 gen(rd());
mt19937 gen(1701);
discrete_distribution<> distr({ 1, 2, 3, 4, 5 });
cout << endl;
cout << "min() == " << distr.min() << endl;
cout << "max() == " << distr.max() << endl;
cout << "probabilities (value: probability):" << endl;
vector<double> p = distr.probabilities();
int counter = 0;
for (const auto& n : p) {
cout << fixed << setw(11) << counter << ": " << setw(14) << setprecision(10) << n << endl;
++counter;
}
cout << endl;
// generate the distribution as a histogram
map<int, int> histogram;
for (int i = 0; i < s; ++i) {
++histogram[distr(gen)];
}
// print results
cout << "Distribution for " << s << " samples:" << endl;
for (const auto& elem : histogram) {
cout << setw(5) << elem.first << ' ' << string(elem.second, ':') << endl;
}
cout << endl;
}
int main()
{
int samples = 100;
cout << "Use CTRL-Z to bypass data entry and run using default values." << endl;
cout << "Enter an integer value for the sample count: ";
cin >> samples;
test(samples);
}
Output
Use CTRL-Z to bypass data entry and run using default values.Enter an integer value for the sample count: 100min() == 0max() == 4probabilities (value: probability): 0: 0.0666666667 1: 0.1333333333 2: 0.2000000000 3: 0.2666666667 4: 0.3333333333Distribution for 100 samples: 0 ::::: 1 :::::::::::::: 2 ::::::::::::::::: 3 :::::::::::::::::::::::::::::: 4 ::::::::::::::::::::::::::::::::::
Requirements
Header: <random>
Namespace: std
discrete_distribution::discrete_distribution
Constructs the distribution.
// default constructor
discrete_distribution();
// constructs using a range of weights, [firstW, lastW)
template <class InputIterator>
discrete_distribution(InputIterator firstW, InputIterator lastW);
// constructs using an initializer list for range of weights
discrete_distribution(initializer_list<double>
weightlist);
// constructs using unary operation function
template <class UnaryOperation>
discrete_distribution(size_t count, double xmin, double xmax, UnaryOperation weightfunc);
// constructs from an existing param_type structure
explicit discrete_distribution(const param_type& parm);
Parameters
firstW
The first iterator in the list from which to construct the distribution.
lastW
The last iterator in the list from which to construct the distribution (non-inclusive because iterators use an empty element for the end).
weightlist
The initializer_list from which to construct the distribution.
count
The number of elements in the distribution range. If count==0, equivalent to the default constructor (always generates zero).
minx
The lowest value in the distribution range.
maxw
The highest value in the distribution range.
weightfunc
The object representing the probability function for the distribution. Both the parameter and the return value must be convertible to double.
parm
The parameter structure used to construct the distribution.
Remarks
The default constructor constructs an object whose stored probability value has one element with value 1. This will result in a distribution that always generates a zero.
The iterator range constructor,
template <class InputIterator>
discrete_distribution(InputIterator firstW, InputIterator lastW);
constructs a distribution object with weights from iterators over the interval sequence [ firstI, lastI).
The initializer list constructor
discrete_distribution(initializer_list<double> weightlist);
constructs a distribution object with weights from the intializer list weightlist.
The constructor defined as
template <class UnaryOperation>
discrete_distribution(size_t count, double xmin, double xmax, UnaryOperation funcweight);
constructs a distribution object whose stored probability value is initialized based on the following rules. If count < 1, n = 1, and as such is equivalent to the default constructor, always generating zero. If count > 0, n = count. Provided 0 < d = ( maxw - minw)/ n, using d uniform subranges each weight is assigned as follows: weightk = weightfunc(x), where x = xmin + k * d + d/ 2, for k = 0, ..., n - 1.
The constructor defined as
explicit discrete_distribution(const param_type& parm);
constructs a distribution object using parm as the stored parameter structure.
discrete_distribution::param_type
Stores all the parameters of the distribution.
struct param_type {
typedef discrete_distribution<IntType> distribution_type;
param_type();
template <class UnaryOperation>
param_type(size_t count, double low, double high, UnaryOperation weightfunc);
std::vector<double>
probabilities() const;
....
bool operator==(const param_type& right) const;
bool operator!=(const param_type& right) const;
};
Parameters
See parent topic discrete_distribution Class.
Remarks
This parameter package can be passed to operator() to generate the return value.