[Rd] .Call and data frames

[Hin-Tak Leung]

I think you want
        else if (TYPEOF(colData) == STRSXP)
... instead.

I don't know if this will convert from factors to string's,
but somewhere it probably involves something like this:
     PROTECT(colData = coerceVector(colData, STRSXP));

Dominick Samperi wrote:
> Hello,
> 
> I'm trying to fetch a data frame through the C API,
> and have no problem doing this when all columns
> are numbers, but when there is a column of
> strings I have a problem. On the C-side the
> function looks like:
> SEXP myfunc(SEXP df),
> and it is called with a dataframe from
> the R side with:
> 
> .Call("myfunc", somedataframe)
> 
> On the C side (actually C++ side) I use code
> like this:
> SEXP colnames = getAttrib(df, R_NamesSymbol)
> cname  = string(CHAR(STRING_ELT(colnames,i))
> SEXP coldata = VECTOR_ELT(df,i) (data for i-th column)
> if(isReal(colData))
>     x = REAL(colData)[j];
> else if(isInteger(colData))
>     i = INTEGER(colData)[j];
> else if(isString(colData))
>     s = CHAR(STRING_ELT(colData,j))
> 
> The problem is that the last test (isString) never passes,
> even when I pass in a frame for which one or more cols
> contain character strings. When the column contains
> strings the isVector(colData) test passes, but no matter
> how I try to fetch the string data I get a seg fault. That
> is, forcing CHAR(STRING_ELT(colData,j)) will
> fault, and so will VECTOR_ELT(colData,0), even
> though colData passes the isVector test.
> 
> Any ideas?
> Thanks,
> ds
> 
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