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

[Carlo de Falco]

On 30 Oct 2009, at 13:27, Guido Walter Pettinari wrote:

> Hi!
>
> Thank you for the answers, Judd & Carlo!
>
> > You can do what you ask by:
> >
> > for ii = 1:N
> > names{ii}  = sprintf("ks_%d", ii);
> > values{ii} = somehow_compute_value (ii);
> > endfor
> >
> > S = cell2struct (values, names, 2)
>
>
> You are right, but the point is that in my code each 'ks_i' is a
> vector of M elements. I am filling all the 'ks_i' vectors inside a
> 'for i=1:M; for i=1:N' nested loop. If I were to call 'cell2struct' in
> each sub-loop, I will obtain many structs, while my idea is to store
> the data in a single struct. I want to obtain a struct 's' such that
> each field 's.ks_i' contains a Mx1 vector (where M is big).

You can still get rid of the eval doing something like the following:

for ii =1:N
names{ii}  = sprintf("ks_%d", ii);
endfor

for jj=1:M
  for ii = 1:N
    KS{ii}(jj) = somehow_compute_value (ii,jj);
  endfor
endfor

S = cell2struct (KS, names, 2)

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}?

> By the way, I solved the issue by memorizing the 'ks_i' into a MxN
> vector called 'ks' inside the loop. Once outside the loop, I filled
> the struct in this way:
>
> for j=1:N
>   eval(  [ 's.k', int2str(j), ' = ks ( :, j );' ]     );
> endfor
>
> In this way I use more memory but the execution is faster.

I expect the option I suggest above to be faster, especially if N is  
big.

> Thank you,
> Guido
>
> P.S. Carlo, is there any reason whereby in your example you used
> sprintf instead of the string concatenation operator [ 'ks_', ii ] ?
> Is the former faster?

I don't know about performance, I just find my syntax more elegant.

c.