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

Am 18.07.22 um 23:03 schrieb Tom Lane:
> I wrote:
>> Martin had originally proposed (2), which I rejected on the grounds
>> that we don't treat multi-dimensional arrays as arrays-of-arrays for
>> any other purpose.
> 
> Actually, after poking at it for awhile, that's an overstatement.
> It's true that the type system doesn't think N-D arrays are
> arrays-of-arrays, but there are individual functions/operators that do.
> Thanks Robert for pointing out the inconsistent behavior of 
array_sample(). That needs to be fixed.

As Tom's investigation showed, there is no consensus in the code if 
multi-dimensional arrays are treated as arrays-of-arrays or not. We need 
to decide what should be the correct treatment.

If we go with (1) array_shuffle() and array_sample() should shuffle each 
element individually and always return a one-dimensional array.

   select array_shuffle('{{1,2},{3,4},{5,6}}');
   -----------
    {1,4,3,5,6,2}

   select array_sample('{{1,2},{3,4},{5,6}}', 3);
   ----------
    {1,4,3}

If we go with (2) both functions should only operate on the first 
dimension and shuffle whole subarrays and keep the dimensions intact.

   select array_shuffle('{{1,2},{3,4},{5,6}}');
   ---------------------
    {{3,4},{1,2},{5,6}}

   select array_sample('{{1,2},{3,4},{5,6}}', 2);
   ---------------
    {{3,4},{1,2}}

I do not feel qualified to make that decision. (2) complicates the code 
a bit, but that should not be the main argument here.

Martin