Re: slow 'eval' function - maybe pointers would do?

[Guido Walter Pettinari]

Dear Jaroslav,

I agree with you: I would never use my approach when the fields are  
more than, say, ~100. However, (i) I need only a few of S.ksi (ii)  
each of them is an array of numbers, not a scalar.

I often access, modify and plot structures' fields at Octave prompt. I  
just feel that addressing the variables with their name (e.g. S.k1)  
rather than with an index (e.g. S.k{1}) is quicker to type and less  
prone to errors. For example, the command:

plot ( S.k1, S.k2, '1x', S.k3, S.k4, '2x )

seems to me more easily typeable and readable than

plot ( S.k{1}, S.k{2}, '1x', S.k{3}, S.k{4}, '2x ).

Just a personal feeling :)

I would like to abuse of your kindness by asking two mailing-list  
questions:

1) When I reply to a mailing-list message, am I supposed to reply to  
the sender of the post as well? For example, should I include your  
personal email-address in the 'to' field?
2) Is it possible to attach text files or images when sending e-mails  
to the mailing list? Are there limits?

Thank you for your consideration.

Regards,

Guido

On Nov 6, 2009, at 9:51 , Jaroslav Hajek wrote:

> On Thu, Nov 5, 2009 at 11:00 PM, Guido Walter Pettinari
> <address@hidden> wrote:
> > Hello everybody!
> >
> > Sorry for this late reply but I had much work to do in these days.
> >
> > Thank you for all the answers. It was very instructive to learn all
> > the methods to handle with field names; I find particularly useful
> > what Benjamin pointed out, that is the possibility to create/access a
> > field via strings by using the parentheses:
> >
> > for i = 1:N
> > field = sprintf ( 'something_%d', i );
> > S.(field) = whatever(i);
> > endfor
> >
> > In this way the structures become really flexible!
> >
> > @Carlo
> > > but still I don't understand why you want to call your vectors
> > > S.ks_ii,
> > > I'm really curious: what's the problem with calling them KS{ii}?
> >
> > I want to call the vectors in that way because I want a struct where
> > the fields are just column vectors. I like to access everything in  
> > the
> > structure S by just typing S.k1 or S.k2 rather than S.KS{i}. This is
> > just a personal preference, probably because I mainly program in C++
> > and I do not feel comfortable with cell arrays yet :)
> >
> > Cheers,
> >
> > Guido
>
> While it probably won't matter until number get really big, you should
> also realize that the syntax
> S.ks{i} is not only more natural (requires no string manipulation
> whatsoever), it is also more efficient.
> When you give S a thousand fields ks1...ks1000, then s.ks200 requires
> a binary search in 1000 strings, while
> s.ks{i} doesn't. Your approach is asymptotically inferior.
> In other words, the arguments for using cell arrays are the same as
> for using arrays of numbers rather than name-mangled scalars.
>
> regards
>
> --
> RNDr. Jaroslav Hajek
> computing expert & GNU Octave developer
> Aeronautical Research and Test Institute (VZLU)
> Prague, Czech Republic
> url: www.highegg.matfyz.cz