Re: [PATCH] Introduce array_shuffle() and array_sample()

> On 29 Sep 2022, at 21:33, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
>
> Martin Kalcher <martin(dot)kalcher(at)aboutsource(dot)net> writes:
>> New patch: array_shuffle() and array_sample() use pg_global_prng_state now.
>
> I took a closer look at the patch today.

Since this seems pretty close to going in, and seems like quite useful
functions, I took a look to see if I could get it across the line (although I
noticed that CFM beat me to the clock in sending this =)).

> I find this behavior a bit surprising:
>
> +SELECT array_dims(array_sample('[-1:2][2:3]={{1,2},{3,NULL},{5,6},{7,8}}'::int[], 3));
> + array_dims
> +-------------
> + [-1:1][2:3]
> +(1 row)
>
> I can buy preserving the lower bound in array_shuffle(), but
> array_sample() is not preserving the first-dimension indexes of
> the array, so ISTM it ought to reset the first lower bound to 1.

I might be daft but I'm not sure I follow why not preserving here, can you
explain?

The rest of your comments have been addressed in the attached v6 I think
(although I'm pretty sure the docs part is just as bad now, explaining these in
concise words is hard, will take another look with fresh eyes tomorrow).

--
Daniel Gustafsson