# Re: [Rd] AS_NUMERIC and as.numeric - Could someone explain?

From: Douglas Bates <bates_at_stat.wisc.edu>
Date: Thu 01 Jul 2004 - 14:09:46 EST

Check, for example,
str(as.numeric(1:100))

Daniel Hoppe wrote:

> Dear List,
>
> I stepped into a strange effect which I can't explain to myself
> (probably due to lack of knowledge on R internals).
>
> I have four vectors a,b,c and z of size 10000 each. With these vectors I
> call
>
> .Call("hyp2f1forrey", a, b, b, z, PACKAGE = "hyp2f1")
>
> to access
>
> SEXP hyp2f1forrey(SEXP a, SEXP b, SEXP c, SEXP x)
> {
> int i,n;
> double *xa, *xb, *xc, *xx, *xresr, *xresi;
> SEXP resr, resi;
>
> n = LENGTH(a);
>
> PROTECT(a = AS_NUMERIC(a));
> PROTECT(b = AS_NUMERIC(b));
> PROTECT(c = AS_NUMERIC(c));
> PROTECT(x = AS_NUMERIC(x));
> PROTECT(resr = NEW_NUMERIC(n));
> PROTECT(resi = NEW_NUMERIC(n));
>
> xa = NUMERIC_POINTER(a);
> xb = NUMERIC_POINTER(b);
> xc = NUMERIC_POINTER(c);
> xx = NUMERIC_POINTER(x);
> xresr = NUMERIC_POINTER(resr);
> xresi = NUMERIC_POINTER(resi);
>
> for (i = 0; i < n; i++)
> F77_CALL(hyp)(&xx[i], &xa[i], &xb[i], &xc[i], &xresr[i],
> &xresi[i]);
> UNPROTECT(6);
> return(resr);
> }
>
> I read the documentation in the way that I could either do the call from
> above or
>
> .Call("hyp2f1forrey", as.numeric(a), as.numeric(b), as.numeric(b),
> as.numeric(z), PACKAGE = "hyp2f1")
>
> and remove the
>
> PROTECT(a = AS_NUMERIC(a));
> PROTECT(b = AS_NUMERIC(b));
> PROTECT(c = AS_NUMERIC(c));
> PROTECT(x = AS_NUMERIC(x));
>
> in the C-Code. What happens now is that in my resulting vector of length
> 10000 some values are incorrect depending on the exact way of calling
> the C-Function.
>
> .Call("hyp2f1forrey", a, b, b, z, PACKAGE = "hyp2f1")[11] -->
> incorrect result
> .Call("hyp2f1forrey", a[11], b[11], b[11]), z[11]), PACKAGE =
> "hyp2f1") --> works
> .Call("hyp2f1forrey", as.numeric(a), as.numeric(b), as.numeric(c),
> as.numeric(z), PACKAGE = "hyp2f1")[11] -- works
> .Call("hyp2f1forrey", a[1:10000], b[1:10000], b[1:10000]),
> z[1:10000]), PACKAGE = "hyp2f1") --> works too!
>
>
> Could someone explain to me where the difference in these calls comes
> from?
>