Re: choosing k elements from a "set", and concat of vecsmall

[Bill Allombert <Bill.Allombert@math.u-bordeaux.fr>]

On Wed, Jul 02, 2025 at 03:32:20PM -0500, Hans L wrote:
> I often have a need to loop over all "n choose k" elements from a set.  The
> closest builtin functionality I have found for this  is to use forsubset,
> and then build a vector from that with vector as follows:
> 
> forsubset([#S,k], s0,
>   my(s = vector(k, i, S[s0[i]]));
>   ...
> );

You can do s = vecextract(S,s0); instead.

> Another somewhat related thing I noticed recently which feels like an
> oversight is when that concat is presented with a t_VEC and t_VECSMALL, it
> just inserts the t_VECSMALL as a single element.
> ? concat([1,2,3],Vecsmall([4,5,6]))
> %12 = [1, 2, 3, Vecsmall([4, 5, 6])]

But this would change the semantic of concat.

Cheers,
Bill.