Alex D Herbert created RNG-62:
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Summary: CombinationSampler
Key: RNG-62
URL: https://issues.apache.org/jira/browse/RNG-62
Project: Commons RNG
Issue Type: New Feature
Reporter: Alex D Herbert
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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