Help with R

Hi Gabor,

On 05-May-05 Gabor Grothendieck wrote:

On 5/5/05, Ted Harding <Ted.Harding at nessie.mcc.ac.uk> wrote:

[...]
However, while representing the raw data in such a form is
well supported by R, it seems to me that extracting data
in a way adapted to different analyses requires users to
create their own methods, using the list-access primitives .

For example, to study the changes in the distribution of
lengths of specimens in relation to Position and Date
(which was one of the important issues in that investigation),
I don't think there are any "list processing" functions
available in R which, given the list-based structure described
above, would allow a simple query of the form

 means( Length , ~ Position:Date , data=Cruise )

It's quite feasible to write one's own; but I think Peter's
hope (expressed in excerpt above) looks like a first call
for thinking about general methods for this sort of thing.

The Green Book defines a recursive apply function, rapply,
that provides a general means of traversing that
sort of structure.
[...]
 R. A. Becker, J. M. Chambers, and A .R. Wilks, The New S Language:
   A Programming Environment for Data Analysis and Statistics.
   Pacific Grove, CA: Wadsworth, 1988. Defines S Version 2, which
   forms the basis of the currently used S Versions 3 and 4, as well
   as R. (Sometimes called the "Blue Book.")

Thanks for your suggestions and comments, Gabor.

However, I now have the Green Book. There is some mention of
'rapply' (pp. 174-5, 371 where the function is used in the
definition of a function, and 430 where it is stated that "The
S and C computations for rapply follow the style of the example
here", the example in question being C code for "a simplified
version of the S function lapply"). However, there is no code
anywhere for rapply itself!

While the above possibly amount to enough hints for a good R
programmer to work out an implementation for rapply, this is at
present a level or two above my skills.

The S-plus code for rapply can be found by listing "rapply".
There are two things wrong with doing this. One is that this
code involves at least two functions which do not seem to
be available in R -- new.frame() and the function which
occurs in .Call(2s_tree_apply", .... ). One would need to
infer what these do and implement them in R.

The other is that I'm not at all keen on the idea of pinching
code from a proprietary product (S-plus).

So I'm wondering if there is any R code that implements the
equivalent of 'rapply' or could readily be extended to do so.