[R] calling C function from R

[Uwe Ligges]

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Wen-Ching Lin wrote:
> Hi,
> 
> I am reading the source code of rpart. I have problems understand the following code and would appreciate for any helps. In rpart.s, there is a line:
> 
> rpfit <- .C(C_s_to_rp,
>             n = as.integer(nobs),
>             nvarx = as.integer(nvar),
>             ncat = as.integer(cats* !isord),
>             method= as.integer(method.int),
>             as.double(unlist(controls)),
>             parms = as.double(unlist(init$parms)),
>             as.integer(xval),
>             as.integer(xgroups),
>             as.double(t(init$y)),
>             as.double(X),
>             as.integer(!is.finite(X)), # R lets Infs through
>             error = character(1),
>             wt = as.double(wt),
>             as.integer(init$numy),
>             as.double(cost),
>             NAOK=TRUE)
> 
> Is this line calling the rpart.c function? 


There is no rpart.c function. It is just a file that contains some C code.
In fact, you should look for the "s_to_rp" entry point.



> If so, what was sent to rpfit? I am confused because rpart.c only returns an integer, not an object. The following is the rpart.c function:
> 
> int rpart(int n,  int nvarx, Sint *ncat, int method,  int  maxpri,  double *parms,  double *ymat,  FLOAT *xmat, Sint *missmat, struct cptable *cptable, struct node **tree,            char **error,   int *which, int xvals,     Sint *x_grp,    double *wt,     double *opt, int ny,  double *cost) 

It is just a declaration.

Uwe Ligges



> ----------------------
> Thanks!
> 
> 
> 
> 
>       
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> 
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