R devel - Oct 2011 - how to return a matrix of strings from c to R ?

I am a bit confused about usage of R internal functions. I am able to send a
char vector from C to R but not sure on how to send a vector of strings etc.

My code looks like this.

<code>

                SEXP result
PROTECT(Rf_allocMatrix(STRSXP,s->n_rics,s->n_fields));

		int i,j;
		for (i=0; i < s->n_rics; i++)
		{
			for (j=0; j < s->n_fields; j++)
			{
				std::string text = s->data[j][i];
				result[j][i] = R_alloc( text.length(), sizeof(char));
				//strcpy(result[j][i], text.c_str());
				SET_STRING_ELT(result[j][i],0,Rf_mkChar(text.c_str()));
			}
		}

//		memcpy(result,s->data.ref(),s->n_fields*s->n_rics*sizeof(200));
		UNPROTECT(1);
		return result;

</code>

Can someone please make me understand this usecase and how to resolve it?

thanks,
Alok

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On Oct 13, 2011, at 3:20 AM, Alok Jadhav wrote:
> I am a bit confused about usage of R internal functions. I am able to send
a
> char vector from C to R but not sure on how to send a vector of strings
etc.
> 
> My code looks like this.
> 
> <code>
> 
>                SEXP result >
PROTECT(Rf_allocMatrix(STRSXP,s->n_rics,s->n_fields));
> 
> 		int i,j;
> 		for (i=0; i < s->n_rics; i++)
> 		{
> 			for (j=0; j < s->n_fields; j++)
> 			{
> 				std::string text = s->data[j][i];
> 				result[j][i] = R_alloc( text.length(), sizeof(char));
> 				//strcpy(result[j][i], text.c_str());
> 				SET_STRING_ELT(result[j][i],0,Rf_mkChar(text.c_str()));
> 			}
> 		}
> 
> //	
memcpy(result,s->data.ref(),s->n_fields*s->n_rics*sizeof(200));
> 		UNPROTECT(1);
> 		return result;
> 
> </code>
> 
> Can someone please make me understand this usecase and how to resolve it?
> 
It's more simple than that:

int rows = s->n_rics, cols = s->n_fields;
SEXP result = PROTECT(Rf_allocMatrix(STRSXP, rows, cols));
for (int i = 0; i < rows; i++) for (int j = 0; j < cols; j++) 
	SET_STRING_ELT(result, i + j * rows, Rf_mkChar(s->data[j][i].c_str()));
UNPROTECT(1);
return result;

Cheers,
Simon


> thanks,
> Alok
> 
> --
> View this message in context:
http://r.789695.n4.nabble.com/how-to-return-a-matrix-of-strings-from-c-to-R-tp3900763p3900763.html
> Sent from the R devel mailing list archive at Nabble.com.
> 
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> R-devel at r-project.org mailing list
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> 
>