R devel - Sep 2005 - NUMERIC_POINTER question

Dear R-developers,

Using .Call I pass a S4 class with e.g. the following class definition:

setClass("mmatrix",representation(
   data="matrix")
)

On the "C side" i do
mat = GET_SLOT(vs,install("data"));
and then:
printf("%f\n",NUMERIC_POINTER(mat)[1]);


The above print statement produces the correct output if 
xx<- new("mmatrix")
xx at data<-matrix(1:12+0.1,3,4). (data is double)

However it prints 
0.0000 
if xx at data are integers ( xx at data<-matrix(1:12,3,4) ).

Can anyone explain it to me why? 
I thought that NUMERIC_POINTER makes it clear that i expect datatype numeric.
(Why otherwise the distinction with INTEGER_POINTER)


cheers
Eryk

On Tue, 13 Sep 2005, nwew wrote:
> Dear R-developers,
> 
> Using .Call I pass a S4 class with e.g. the following class definition:
> 
> setClass("mmatrix",representation(
>    data="matrix")
> )
> 
> On the "C side" i do
> mat = GET_SLOT(vs,install("data"));
> and then:
> printf("%f\n",NUMERIC_POINTER(mat)[1]);
> 
> 
> The above print statement produces the correct output if 
> xx<- new("mmatrix")
> xx at data<-matrix(1:12+0.1,3,4). (data is double)
> 
> However it prints 
> 0.0000 
> if xx at data are integers ( xx at data<-matrix(1:12,3,4) ).
> 
> Can anyone explain it to me why? 
> I thought that NUMERIC_POINTER makes it clear that i expect datatype
numeric.
> (Why otherwise the distinction with INTEGER_POINTER)
No, I think you have to make sure that the bits are in the correct mode. 
Could you use validation at the new() to do it? A matrix could be double, 
integer, logical or character at least, but on the C side you only want 
double. I don't think expectations come into it.

Roger
> 
> 
> cheers
> Eryk
> 
> ______________________________________________
> R-devel at r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-devel
> 
-- 
Roger Bivand
Economic Geography Section, Department of Economics, Norwegian School of
Economics and Business Administration, Helleveien 30, N-5045 Bergen,
Norway. voice: +47 55 95 93 55; fax +47 55 95 95 43
e-mail: Roger.Bivand at nhh.no

You have to coerce to numeric yourself if that's what you want. Eg in the R
code, as.numeric(1:12) rather than 1:12. Or check the type first in C with
TYPEOF before doing NUMERIC_POINTER or INTEGER_POINTER (the difference is
that the two do different casts; they both point a fixed offset into the R
data structure and I'm not sure if there's a guarantee that this offset
needs to be the same, so perhaps the two don't even point to the same
location...).

Reid Huntsinger

-----Original Message-----
From: r-devel-bounces at r-project.org [mailto:r-devel-bounces at r-project.org]
On Behalf Of nwew
Sent: Tuesday, September 13, 2005 2:26 PM
To: r-devel
Subject: [Rd] NUMERIC_POINTER question


Dear R-developers,

Using .Call I pass a S4 class with e.g. the following class definition:

setClass("mmatrix",representation(
   data="matrix")
)

On the "C side" i do
mat = GET_SLOT(vs,install("data"));
and then:
printf("%f\n",NUMERIC_POINTER(mat)[1]);


The above print statement produces the correct output if 
xx<- new("mmatrix")
xx at data<-matrix(1:12+0.1,3,4). (data is double)

However it prints 
0.0000 
if xx at data are integers ( xx at data<-matrix(1:12,3,4) ).

Can anyone explain it to me why? 
I thought that NUMERIC_POINTER makes it clear that i expect datatype
numeric.
(Why otherwise the distinction with INTEGER_POINTER)


cheers
Eryk

______________________________________________
R-devel at r-project.org mailing list
https://stat.ethz.ch/mailman/listinfo/r-devel

Eryk,

On Sep 13, 2005, at 2:26 PM, nwew wrote:
> printf("%f\n",NUMERIC_POINTER(mat)[1]);
> [...]
> However it prints
> 0.0000
> if xx at data are integers ( xx at data<-matrix(1:12,3,4) ).
>
> Can anyone explain it to me why?
> I thought that NUMERIC_POINTER makes it clear that i expect  
> datatype numeric.
> (Why otherwise the distinction with INTEGER_POINTER)
You answered your own question - NUMERIC_POINTER expects that the  
SEXP you pass to it is numeric=double. When you use it, it's your  
responsibility to make sure that the SEXP is numeric and not integer  
or anything else. Probably you may want to use AS_NUMERIC to ensure  
that. [btw: NUMERIC_POINTER() is a compatibility macro for REAL() and  
AS_NUMERIC(x) for coerceVector(x,REALSXP)].

Also you should be aware that C uses 0-based indices so  
NUMERIC_POINTER(mat)[1] accesses the 2nd element of the vector.

Cheers,
Simon