Package org.apache.commons.rng.sampling

Class CombinationSampler

java.lang.Object

org.apache.commons.rng.sampling.CombinationSampler

public class CombinationSampler
extends java.lang.Object

Class for representing combinations of a sequence of integers.

A combination is a selection of items from a collection, such that (unlike permutations) the order of selection does not matter. This sampler can be used to generate a combination in an unspecified order and is faster than the corresponding PermutationSampler.

Note that the sample order is unspecified. For example a sample combination of 2 from 4 may return [0,1] or [1,0] as the two are equivalent, and the order of a given combination may change in subsequent samples.

The sampler can be used to generate indices to select subsets where the order of the subset is not important.

See Also:

PermutationSampler

Constructor Summary

Constructors

Constructor	Description
CombinationSampler(org.apache.commons.rng.UniformRandomProvider rng, int n, int k)	Creates a generator of combinations.

Method Summary

Modifier and Type	Method	Description
int[]	sample()	Return a combination of k whose entries are selected randomly, without repetition, from the integers 0, 1, ..., n-1 (inclusive).

Methods inherited from class java.lang.Object

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

Constructor Detail

CombinationSampler

public CombinationSampler(org.apache.commons.rng.UniformRandomProvider rng,
                          int n,
                          int k)

Creates a generator of combinations.

The sample() method will generate an integer array of length k whose entries are selected randomly, without repetition, from the integers 0, 1, ..., n-1 (inclusive). The returned array represents a combination of n taken k.

In contrast to a permutation, the returned array is not guaranteed to be in a random order. The sample() method returns the array in an unspecified order.

If n <= 0 or k <= 0 or k > n then no combination is required and an exception is raised.

Parameters:

rng - Generator of uniformly distributed random numbers.

n - Domain of the combination.

k - Size of the combination.

Throws:

java.lang.IllegalArgumentException - if n <= 0 or k <= 0 or k > n.

Method Detail

sample

public int[] sample()

Return a combination of k whose entries are selected randomly, without repetition, from the integers 0, 1, ..., n-1 (inclusive).

The order of the returned array is not guaranteed to be in a random order as the order of a combination does not matter.

Returns:

a random combination.