Horton

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

David G. Johnston <david.g.johnston@gmail.com>

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From: "David G. Johnston" <david.g.johnston@gmail.com>
To: Tom Lane <tgl@sss.pgh.pa.us>
Cc: Martin Kalcher <martin.kalcher@aboutsource.net>, Robert Haas <robertmhaas@gmail.com>, John Naylor <john.naylor@enterprisedb.com>, Thomas Munro <thomas.munro@gmail.com>, PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>
Date: 2022-07-18T22:32:00Z
Lists: pgsql-hackers, pgsql-general 
On Mon, Jul 18, 2022 at 3:18 PM Tom Lane <tgl@sss.pgh.pa.us> wrote:

>
> Independently of the dimensionality question --- I'd imagined that
> array_sample would select a random subset of the array elements
> but keep their order intact.  If you want the behavior shown
> above, you can do array_shuffle(array_sample(...)).  But if we
> randomize it, and that's not what the user wanted, she has no
> recourse.
>
>
And for those that want to know in what order those elements were chosen
they have no recourse in the other setup.

I really think this function needs to grow an algorithm argument that can
be used to specify stuff like ordering, replacement/without-replacement,
etc...just some enums separated by commas that can be added to the call.

David J.

Commits

  1. Add array_sample() and array_shuffle() functions.

  2. Use a separate random seed for SQL random()/setseed() functions.