Waiting for PostgreSQL 16 – Add array_sample() and array_shuffle() functions.

On 7th of April 2023, Tom Lane committed patch:

Add array_sample() and array_shuffle() functions.
These are useful in Monte Carlo applications.
Martin Kalcher, reviewed/adjusted by Daniel Gustafsson and myself
Discussion: https://postgr.es/m/9d160a44-7675-51e8-60cf-6d64b76db831@aboutsource.net

Arrays are supported in PostgreSQL since forever, documentation for Pg15 lists 18 functions. And now, we're getting two more:

  • array_sample() – get some (one or more) random elements from given array
  • array_shuffle() – to randomize order of elements in given array

Let's see how that works:

$ SELECT array_sample('{a,b,c,d,e,f,g,h,i,j,k}'::text[], 1);
(1 ROW)
$ SELECT array_sample('{a,b,c,d,e,f,g,h,i,j,k}'::text[], 5);
(1 ROW)

If you'd pick sample size (second argument) that is larger than source table, you will get an error:

$ SELECT array_sample('{a,b,c,d,e,f,g,h,i,j,k}'::text[], 20);
ERROR:  sample SIZE must be BETWEEN 0 AND 11

As for array_shuffle, it's work is pretty obvious:

$ SELECT array_shuffle('{a,b,c,d,e,f,g,h,i,j,k}'::text[]);
(1 ROW)

In case of multi-dimensional arrays, the shuffling happens on first dimension, that is sub-arrays will remain in their original order:

$ SELECT array_sample( '{{a,b,c},{d,e,f},{g,h,i},{j,k,l},{m,n,o}}'::text[][], 3 );
(1 ROW)
$ SELECT array_shuffle( '{{a,b,c},{d,e,f},{g,h,i},{j,k,l},{m,n,o}}'::text[][] );
(1 ROW)

Pretty cool. Now, if we only could get official, in core, array_sort, array_unique, that would be awesome 🙂

Anyway, these two functions are definitely useful, so thanks a lot to everyone involved.

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