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https://issues.apache.org/jira/browse/RNG-184?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Alex Herbert resolved RNG-184.
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Resolution: Implemented
Updated to return a reference to the input array in commit:
9951b22e5ca412c8388fcca3e78c08ecc06eae49
> ArraySampler to shuffle all primitive array types and generic T[] arrays
> ------------------------------------------------------------------------
>
> Key: RNG-184
> URL: https://issues.apache.org/jira/browse/RNG-184
> Project: Commons RNG
> Issue Type: New Feature
> Components: sampling
> Affects Versions: 1.5
> Reporter: Alex Herbert
> Assignee: Alex Herbert
> Priority: Major
> Fix For: 1.6
>
>
> The sampling module contains code to shuffle int[] in the PermutationSampler:
> {code:java}
> public static void shuffle(UniformRandomProvider rng, int[] list)
> public static void shuffle(UniformRandomProvider rng,
> int[] list,
> int start,
> boolean towardHead) {code}
> 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:
> {code:java}
> public static void shuffle(UniformRandomProvider rng, int[] data);
> public static void shuffle(UniformRandomProvider rng, int[] data,
> int from, int to);
> {code}
> Note that there is a ListSampler that offers similar functionality for a List:
> {code:java}
> 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)
> {code}
> I do not think supporting a range for shuffling here is required as this can
> be achieved using:
> {code:java}
> int from = ...
> int to = ...
> ListSampler.shuffle(rng, list.subList(from, to));
> {code}
> 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.:
> {code:java}
> public static double[] sample(UniformRandomProvider rng,
> double[] array,
> int k) {
> public static <T> T[] sample(UniformRandomProvider rng,
> T[] array,
> int k)
> {code}
> 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.
> {code:java}
> // Sampler returns k elements from the given array
> SharedStateObjectSampler<double[]> createSampler(UniformRandomProvider rng,
> double[] array, int k).{code}
> Such a sampler would internally maintain the PermutationSampler between
> invocations.
> This ticket will only cover shuffling support in ArraySampler.
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