Re: Python combinations() in GP?

[Aurel Page <aurel.page@normalesup.org>]

Dear Hermann,

What you want is probably flag=2 in forvec.

Cheers,
Aurel

On 06/09/2023 13:14, hermann@stamm-wilbrandt.de wrote:
> I am porting Python code to GP.
>
> I need Python combinations from itertools:
>
> > > > from itertools import combinations
> > > > for i in combinations(range(5),3):
> ...     print(i)
> ...
> (0, 1, 2)
> (0, 1, 3)
> (0, 1, 4)
> (0, 2, 3)
> (0, 2, 4)
> (0, 3, 4)
> (1, 2, 3)
> (1, 2, 4)
> (1, 3, 4)
> (2, 3, 4)
> > > >
>
> Since GP is 1-based and not 0-based at Python, I came up with this:
>
> $ cat part.gp
> sorted(v)=
> {
>   if(#v<2,return(1));
>   if(v[1]>=v[2],return(0));
>   sorted(v[2..#v]);
> }
>
> {
>   forvec(v=vector(3,i,[1,5]),
>     if(sorted(v),
>       print(v)));
> }
> $
>
> Which does the right output, but has to skip many not sorted 
> combinations.
> Is there a more efficient GP code for Python combinations?
>
> $ gp -q < part.gp
> [1, 2, 3]
> [1, 2, 4]
> [1, 2, 5]
> [1, 3, 4]
> [1, 3, 5]
> [1, 4, 5]
> [2, 3, 4]
> [2, 3, 5]
> [2, 4, 5]
> [3, 4, 5]
> $
>
>
> Regards,
>
> Hermann.