[Rd] .Call - applying setAttrib(x, R_DimSymbol, s) to a matrix being an element of a list

Oleg Sklyar osklyar at ebi.ac.uk
Wed Mar 16 18:40:54 CET 2005

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

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

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