[R] getAttrb - Solved
kohnicho at comp.nus.edu.sg
Thu Sep 7 09:32:41 CEST 2000
I think what I found confusing is the extsenion writers manual states
"What happens if we want to add an attribute that is not pre-dened? We
need to add a symbol for it via a call to install. Suppose for
wanted to add an attribute "version" with value 3.0. We could use
PROTECT(version = allocVector(REALSXP, 1));
REAL(version) = 3.0;
setAttrib(ans, install("version"), version);
So I assumed install was to install the attribute name in the symbol table
but not to retrieve it. Maybe a little clarification there would help such
as "intall can also be used in getAttrib() to retrive an attribute
installed in the sybol table"
On Thu, 7 Sep 2000, Prof
> On Thu, 7 Sep 2000, Nicholas Lewin-Koh wrote:
> > Hi,
> > I changed
> > INTEGER(getAttrib(shape,mkChar("nParts")))
> > to
> > INTEGER(getAttrib(shape,mkString("nParts")))
> > and now it works fine.
> In `Writing R Extensions' you would have seen that the second argument of
> getAttrib (and setAttrib) is the name in the symbol table, and the way to
> get that is install("nParts"). (Towards the end of section 3.6.4.) The
> first line of getAttrib is in fact
> if (isString(name)) name = install(CHAR(STRING_ELT(name, 0)));
> which shows that mkString is immediately being undone.
> These internals are not very extensively documented, but this call was.
> In other cases, look at the usage in the code of R itself (src/main/*.c)
> for clarification.
> Brian D. Ripley, ripley at stats.ox.ac.uk
> Professor of Applied Statistics, http://www.stats.ox.ac.uk/~ripley/
> University of Oxford, Tel: +44 1865 272861 (self)
> 1 South Parks Road, +44 1865 272860 (secr)
> Oxford OX1 3TG, UK Fax: +44 1865 272595
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