[R] Object-oriented programming in R

Mark Wardle mark at wardle.org
Thu May 28 09:13:14 CEST 2009

Hi. I remember considering these options myself but concluded that for
most analyses a strictly procedural approach was satisfactory.
Although I may re-run multiple analyses, the data manipulation (and
subsequent analysis - the former always more complex than the latter
IMHO) is fairly project- and data-specific. As such, quick and
specific code always seemed more appropriate than slow (to write) and

Obviously that doesn't apply to package creators and maintainers,
creating something that is going to re-used in many different projects
and can be made generic. That's the heuristic I now use - is this good
enough for other people's consumption - if so, create a package and
adopt some of the OO approaches seen in the base R packages.
Otherwise, stick to bespoke and specific (procedural) functions.

I've a small library of helper functions, but these don't use OO
usually. They sometimes make assumptions about data passed in, don't
have particularly robust error checking, but in general, work well. I
suppose it depends on what you're trying to achieve and how much time
you've got!

Interested in other's thoughts too as clearly there's no "right answer" here.



2009/5/27 Luc Villandre <villandl at dms.umontreal.ca>:
> Dear R-users,
> I have very recently started learning about object-oriented programming in
> R. I am far from being an expert in programming, although I do have an
> elementary C++ background.
> Please take a look at these lines of code.
>> some.data = data.frame(V1 = 1:5, V2 = 6:10) ;
>> p.plot = ggplot(data=some.data,aes(x=V1, y=V2)) ;
>> class(p.plot) ;
>> [1] "ggplot"
> My understanding is that the object p.plot belongs to the "ggplot" class.
> However, a new class definition like
>> setClass("AClass", representation(mFirst = "numeric", mSecond = "ggplot"))
>> ;
> yields the warning
>> Warning message:
>> In .completeClassSlots(ClassDef, where) :
>>  undefined slot classes in definition of "AClass": mSecond(class "ggplot")
> The ggplot object is also a list :
>> is.list(p.plot)
>> [1] TRUE
> So, I guess I could identify mSecond as being a list.
> However, I don't understand why "ggplot" is not considered a valid slot
> type. I thought setClass() was analogous to the class declaration in C++,
> but I guess I might be wrong. Would anyone care to provide additional
> explanations about this?
> I decided to explore object-oriented programming in R so that I could
> organize the output from my analysis in a more rigorous fashion and then
> define custom methods that would yield relevant output. However, I'm
> starting to wonder if this aspect is not better suited for package builders.
> R lists are already very powerful and convenient templates. Although it
> wouldn't be as elegant, I could define functions that would take lists
> outputted by the different steps of my analysis and do what I want with
> them. I'm wondering what the merits of both approaches in the context of R
> would be. If anyone has any thoughts about this, I'd be most glad to read
> them.
> Cheers,
> --
> *Luc Villandré*
> /Biostatistician
> McGill University Health Center -
> Montreal Children's Hospital Research Institute/
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Dr. Mark Wardle
Specialist registrar, Neurology
Cardiff, UK

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