Package org.apache.commons.rng.sampling

Class 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.

    Sampling uses UniformRandomProvider.nextInt(int).

    See Also:
    PermutationSampler

    • 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​(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.