[R] Accessing row and col names of SEXP objects

[Prof Brian Ripley]

>From the file defining GetColNames:

/* "GetRowNames" and "GetColNames" are utility routines which
 * locate and return the row names and column names from the
 * dimnames attribute of a matrix.  They are useful because

You have not applied them to the dimnames attribute.  Extracting 
dimnames attributes _is_ covered in R-exts:

SEXP dimnames=getAttrib(ts, R_DimNamesSymbol), 
     colnames = VECTOR_ELT(dimnames, 1);

for (j = 0; j < length(colnames); j++) 
   printf("%s\n",CHAR(STRING_ELT(colnames, j)));

looks about right, although you should do something if the colnames or 
dimnames are NULL.

On Wed, 17 Dec 2003, Whit Armstrong wrote:

> Can someone lend me a hand with extracting the dimnames from a SEXP?  I've
> looked through R-exts, but I couldn't find an example.
> 
> Here is the code I'm using to grab the jth column name and print it, but the
> colnames I'm getting are garbage.
> 
> None of the following are working.
> 
> void printInfo(SEXP ts) {
> 
> int j;
> 
> for (j=0; j<col; j++) {
>   	printf("%s\n",CHAR(STRING_ELT(GetColNames(ts), j)));
> 	printf("%s\n",CHAR(VECTOR_ELT(GetColNames(ts), j)));
> 	printf("%s\n",CHARACTER_DATA(STRING_ELT(GetColNames(ts), j)));
> 	printf("%s\n",CHARACTER_DATA(VECTOR_ELT(GetColNames(ts), j)));
>   }
> 
> }
> 
> Here is the object I'm passing in:
> 	
> 	tmp <- matrix(rnorm(100),ncol=5)
> 	colnames(tmp) <- c("tmp","a","b","c","d")
> 	rownames(tmp) <- 1:100	
> 	.Call("printInfo",tmp)
> 
> Thanks for your help.
> 
> Regards,
> Whit
> 
> ______________________________________________
> R-help at stat.math.ethz.ch mailing list
> https://www.stat.math.ethz.ch/mailman/listinfo/r-help
> 
> 

-- 
Brian D. Ripley,                  ripley at stats.ox.ac.uk
Professor of Applied Statistics,  http://www.stats.ox.ac.uk/~ripley/
University of Oxford,             Tel:  +44 1865 272861 (self)
1 South Parks Road,                     +44 1865 272866 (PA)
Oxford OX1 3TG, UK                Fax:  +44 1865 272595