Re: Two suggestions:

["Karim Belabas" <belabas@math.u-bordeaux1.fr>]

* John Cremona [2006-01-18 17:31]:
> (2) The elliptic curve databes holds each curve's id as a string, for
> example "20160cy2".  It would be convenient to be able to simply split
> this into 3 components, for example [20160,"cy",2].  With Bill's help I
> have written a gp function to do this:
> 
> {
> code2seq(code)=local(v,N=0,num=0,i=1,i1,class);
> v=Vecsmall(code);
> while(v[i]<58,N=10*N+v[i]-48;i++);
> i1=i;
> while(v[i]>57,i++);
> class=Strchr(vector(i-i1,j,v[i1+j-1]));
> while(i<=length(v),num=10*num+v[i]-48;i++);
> [N,class,num]
> }
> 
> But this direct manipulation of the vector of ASCII codes is rather
> awkward.   Surely there would be other places in which some string
> manipulation would be helpful?  Can we add this to the wish-list please?

An off-topic answer, which might be useful in another context; using
a high-level external filter is a good alternative:

 code2seq(code) =
 {
   extern("echo " code "|perl -ne 'm/([0-9]+)([a-z]+)([0-9]+)/;
                                   print \"[$1,\\\"$2\\\",$3]\" ' ")
 }

(20:16) gp > code2seq("20160cy2")
%1 = [20160, "cy", 2]

Cheers,

    Karim.

P.S: for more complicated processing, an external script will be cleaner of
course, it's a pain to escape all those quotes and backslashes. Also, my
variant is unfortunately orders of magnitude slower than your "awkward"
approach.
-- 
Karim Belabas                  Tel: (+33) (0)5 40 00 26 17
Universite Bordeaux 1          Fax: (+33) (0)5 40 00 69 50
351, cours de la Liberation    http://www.math.u-bordeaux.fr/~belabas/
F-33405 Talence (France)       http://pari.math.u-bordeaux.fr/  [PARI/GP]