partialShuffle only shuffles subset.

[Joseph Rushton Wakeling via Digitalmars-d-learn]

On Tuesday, 19 May 2015 at 14:31:21 UTC, Ivan Kazmenko wrote:
> On Tuesday, 19 May 2015 at 10:00:33 UTC, BlackEdder wrote:
>> The documentation seems to indicate that partialShuffle: 
>> Partially shuffles the elements of r such that upon returning 
>> r[0..n] is a random subset of r, (which is what I want), but 
>> it seems that partialShuffle actually only shuffles the first 
>> subset of the range (which you could do probably also do by 
>> [0..n].randomShuffle).
>>
>> This different behaviour was problem created since: 
>> https://issues.dlang.org/show_bug.cgi?id=11738. Does anyone 
>> know what the intended behaviour is/was?
>
> Reading the current documentation and unittests, I now also 
> believe the fix was a mistake.  Reopened the issue for now with 
> a comment: https://issues.dlang.org/show_bug.cgi?id=11738#c2
>
> I hope Joseph Rushton Wakeling looks into it soon.

Reading the documentation it does appear that the function 
behaviour is at odds with what is described.  I don't know how I 
came to that misunderstanding.

In the short term, if you want a randomly-shuffled random subset 
of a range, you could get it via something like,

     original_range.randomSample(n).array.randomShuffle;

or maybe better

     original_range.randomShuffle.randomSample(n);