[R] I can't make .C(...) web-page example.

[Uwe Ligges]

Ricardo Zorzetto Nicoliello Vencio wrote:

> Hi everyone!
> 
> I'm trying to lear how to call external C code in R but even the R help
> web-page example is drive me crazy.
> 
> I copy-paste the example at:
> 
> http://stat.ethz.ch/R-manual/R-patched/doc/manual/R-exts.html#Interface%20functions%20.C%20and%20.Fortran
> 
> here is the example:
> 
> void convolve(double *a, int *na, double *b, int *nb, double *ab)
> {
>   int i, j, nab = *na + *nb - 1;
> 
>   for(i = 0; i < nab; i++)
>     ab[i] = 0.0;
>   for(i = 0; i < *na; i++)
>     for(j = 0; j < *nb; j++)
>       ab[i + j] += a[i] * b[j];
> }
> 
> called from R by
> 
> conv <- function(a, b)
>   .C("convolve",
>      as.double(a),
>      as.integer(length(a)),
>      as.double(b),
>      as.integer(length(b)),
>      ab = double(length(a) + length(b) - 1))$ab
> 
> 
> but using the conv function in simple examples give me trouble:
> 
> 
> conv(1:10,2:11)
 >
> Error in conv(1:10, 2:11) : pairlist object cannot be coerced to double
> 
> 
>>conv( rnorm(10,10,1) , rnorm(10,11,1) )
> 
> Segmentation fault
> 
> 
>>conv( c(10.53, 8.456, 6.6) , c(10.53, 8.456, 6.6) )
> 
> Error in conv(c(10.53, 8.456, 6.6), c(10.53, 8.456, 6.6)) :
>         cannot allocate vector of length 1717986918
> 
> 
>>a = c(1.46756, 5.56456, 2.3646)
>>b = a + 5.4
>>conv(a,b)
> 
> Error in conv(a, b) : cannot coerce type promise to double vector
> 
> 
> and so on.
> 
> These results appear if I have only the .c file or if I use gcc -c conv.c
> to create .o file. I cannot create executable because there is no
> main(...) in .c file but just the copy-pasted example.

Most easily, use the R wrapper to compile and link files as in:

R CMD SHLIB convolve.c
which produces an .so file you can dyn.load().
(If you are on Windows: Rcmd SHLIB makes a dll.)

Uwe Ligges


> 
> Someone knows what is happening to me ?
> 
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