[Rd] OOP performance, was: V2.9.0 changes

[Thomas Petzoldt]

Hi Troy,

first of all a question, what kind of ecosystem models are you
developing in R? Differential equations or individual-based?

Your write that you are a frustrated Java developer in R. I have a
similar experience, however I still like JAVA, and I'm now more happy
with R as it is much more efficient (i.e. sum(programming + runtime))
for the things I usually do: ecological data analysis and modelling.

After using functional R quite a time and Java in parallel
I had the same idea, to make R more JAVA like and to model ecosystems in
an object oriented manner. At that time I took a look into R.oo (thanks
Henrik Bengtssson) and was one of the Co-authors of proto. I still think
that R.oo is very good and that proto is a cool idea, but finally I
switched to the recommended S4 for my ecological simulation package.

Note also, that my solution was *not* to model the ecosystems as objects
(habitat - populations- individuals), but instead to model ecological
models (equations, inputs, parameters, time steps, outputs, ...).

This works quite well with S4. A speed test (see useR!2006 poster on
http://simecol.r-forge.r-project.org/) showed that all OOP flavours had
quite comparable performance.

The only thing I have to have in mind are a few rules:

- avoid unnecessary copying of large objects. Sometimes it helps to
prefer matrices over data frames.

- use vectorization. This means for an individual-based model that one
has to re-think how to model an individual: not "many [S4] objects"
like in JAVA, but R structures (arrays, lists, data frames) where
vectorized functions (e.g. arithmetics or subset) can work with.

- avoid interpolation (i.e. approx) and if unavoidable, minimize the tables.

If all these things do not help, I write core functions in C (others use
Fortran). This can be done in a mixed style and even a full C to C
communication is possible (see the deSolve documentation how to do this
with differential equation models).


Thomas P.



-- 
Thomas Petzoldt
Technische Universitaet Dresden
Institut fuer Hydrobiologie        thomas.petzoldt at tu-dresden.de
01062 Dresden                      http://tu-dresden.de/hydrobiologie/
GERMANY