R devel - Mar 2005 - .Call - applying setAttrib(x, R_DimSymbol, s) to a matrix being an element of a list

Dear R developers,

I am writing some C code that loads multiple images into a list of R 
matrices. The whole R object is created within the C code. To simplify 
coding, elements of the list are first created as vectors and then 
converted to corresponding matrices using setAttrib(x, R_DimSymbol, s). 
Generally the code works fine except for one detail. Applying setAttrib 
sets ALL elements (matrices) in the list to the same size, namely to the 
one last applied, doesn't matter if other matrices are larger or 
smaller. The command is applied to an element, not to the whole list in 
the following way, see below. Is there any way to change the dims of an 
element without altering other elements in this example? Furthermore, if 
I skip the last command and return a list of vectors instead of a list 
of matrices - all vectors have different lengths corresponding to the 
respective image sizes.

// creating the list to hold matrices
SEXP result = allocVector(VECSXP, nFiles);

// creating a vector for the list element i
SET_VECTOR_ELT(result, i, allocVector(INTSXP, size[0] * size[1]));

// getting a pointer to the element to simlify coding
SEXP element = VECTOR_ELT(result, i);

// writing some values to the element

// converting element into a matrix
setAttrib(element, R_DimSymbol, imgSize);

Thanks in advance for help
Oleg

Dr Oleg Sklyar
European Bioinformatics Institute
Wellcome Trust Genome Campus
Hinxton, Cambridge, CB10 1SD
England
phone/fax  +44(0)1223 49 4478/4468
e-mail osklyar@ebi.ac.uk

Oleg,

you gave us only a fragment of your code, so I can only guess what the 
problem is:

On Mar 16, 2005, at 12:40 PM, Oleg Sklyar wrote:
> // converting element into a matrix
> setAttrib(element, R_DimSymbol, imgSize);
What is imgSize? The behavior you describe seems as if you re-using the 
imgSize SEXP in all elements. AFAIR in your case setAttrib doesn't copy 
the value, so you need to do so yourself (or alloc new dim array for 
each element).

Cheers,
Simon