Major Description
The sampling module contains code to shuffle int[] in the PermutationSampler:
public static void shuffle(UniformRandomProvider rng, int[] list) public static void shuffle(UniformRandomProvider rng, int[] list, int start, boolean towardHead)
Shuffling support should be expanded to all primitive types and a generic array type.
The non-integer domain is out of scope for the PermutationSampler. The shuffle method is present as a utility for permuting arrays of indices.
I suggest a new API in ArraySampler with a shuffle that can handle sub-ranges as:
public static void shuffle(UniformRandomProvider rng, int[] data); public static void shuffle(UniformRandomProvider rng, int[] data, int from, int to);
Note that there is a ListSampler that offers similar functionality for a List:
public static <T> void shuffle(UniformRandomProvider rng, List<T> list) public static <T> void shuffle(UniformRandomProvider rng, List<T> list, int start, boolean towardHead) // Also sampling public static <T> List<T> sample(UniformRandomProvider rng, List<T> collection, int k)
I do not think supporting a range for shuffling here is required as this can be achieved using:
int from = ... int to = ... ListSampler.shuffle(rng, list.subList(from, to));
This is the how the half-shuffle method (towards head/tail) is implemented. The origin of the half-shuffle API is unknown but it is not as flexible a sub-range shuffle and I do not propose to implement it for all array types.
Note that consistency between Lists and arrays would require a sampling method for all arrays, e.g.:
public static double[] sample(UniformRandomProvider rng, double[] array, int k) { public static <T> T[] sample(UniformRandomProvider rng, T[] array, int k)
Since this static method uses a new PermutationSampler per sample the method is not suitable for repeat invocation. Development of a sampling API for arrays should be under another ticket, e.g.
// Sampler returns k elements from the given array SharedStateObjectSampler<double[]> createSampler(UniformRandomProvider rng, double[] array, int k).
Such a sampler would internally maintain the PermutationSampler between invocations.
This ticket will only cover shuffling support in ArraySampler.
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Issue Links
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RNG-185 ArraySampler to have factory methods to sample from arrays
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