[jira] [Resolved] (RNG-62) CombinationSampler

["Gilles (JIRA)" <ji...@apache.org>]

     [ https://issues.apache.org/jira/browse/RNG-62?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Gilles resolved RNG-62.
-----------------------
       Resolution: Implemented
    Fix Version/s: 1.2

commit 17ddb9f3376a1cc2e798246fedcf73320902354c

> CombinationSampler
> ------------------
>
>                 Key: RNG-62
>                 URL: https://issues.apache.org/jira/browse/RNG-62
>             Project: Commons RNG
>          Issue Type: New Feature
>            Reporter: Alex D Herbert
>            Priority: Minor
>             Fix For: 1.2
>
>
> The sampling module contains a PermutationSampler. There is scope to create a CombinationSampler too.
> [https://en.wikipedia.org/wiki/Permutation]
> [https://en.wikipedia.org/wiki/Combination]
> If the order of the returned sample is not important then a combination can be generated faster than a permutation. 
> The sample can be optimised by only performing the first k or (n-k) steps from a full Fisher-Yates shuffle from the end of the domain to the start. The upper positions will then contain a random permutation sample from the domain. The lower half is then by definition also a random sample (just not in a random order). The sample is then picked using the upper or lower half depending which makes the number of steps smaller.



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