On Jul 15, 2008, at 12:00 PM, Duncan Murdoch wrote:
On 7/15/2008 2:11 PM, Kasper Daniel Hansen wrote:
Using
> methods("plot")
[1] plot.Date* plot.HoltWinters* plot.POSIXct*
[4] plot.POSIXlt* plot.TukeyHSD plot.acf*
[7] plot.data.frame* plot.decomposed.ts* plot.default
[10] plot.dendrogram* plot.density plot.ecdf
[13] plot.factor* plot.formula* plot.hclust*
[16] plot.histogram* plot.isoreg* plot.lm
[19] plot.medpolish* plot.mlm plot.ppr*
[22] plot.prcomp* plot.princomp* plot.profile.nls*
[25] plot.spec plot.spec.coherency plot.spec.phase
[28] plot.stepfun plot.stl* plot.table*
[31] plot.ts plot.tskernel*
Non-visible functions are asterisked
I don't see plot.function listed. As I read the man page for
methods I would say that the search is just looking for functions
with the right type of name.
In a package with a NAMESPACE (like the graphics package, where
plot.function lives), a function needs to be declared to be an
S3method to show up in this list. plot.function is not declared as
an S3 method.
I don't know the reason for this, but I assume it's intentional:
take a look at the plot() generic: it has special case code to
handle functions.
Let me just state that if I do
plot(sin)
plot.function gets called. This looks to me (as a somewhat experienced
R user) as a clear case of method dispatching. I call something that I
think most of us think of as a generic, with a function argument and I
cannot see that possibility when I do a methods("plot"). This use case
is not entirely far out - I have just been teaching and wanted to show
how I could see what happened when I called plot on sin and lo and
behold, plot.function is not in the list of methods("plot")
I can see that there is special code in plot for handling dispatching
on a function. I can see that is it handled differently (ie. not with
a call to UseMethod) but from my point of view, the call
plot(sin)
looks and feels like methods dispatching. I would say plot is a generic.
Finally the help page for plot.function states
## S3 method for class 'function':
plot(x, y = 0, to = 1, from = y, xlim = NULL, ...)
So I think something should be cleaned up here.
Kasper
So if this is a bug, I think it's a documentation bug in the ?
plot.function man page, where plot.function should be documented to
act a lot like an S3 method, but not identically like one: notice
the special handling of the y axis label.
If I define a plot.function in my global workspace,
methods("plot") picks it up
> plot.function = function() {print("blah")}
> methods("plot")
[1] plot.Date* plot.HoltWinters* plot.POSIXct*
[4] plot.POSIXlt* plot.TukeyHSD plot.acf*
[7] plot.data.frame* plot.decomposed.ts* plot.default
[10] plot.dendrogram* plot.density plot.ecdf
[13] plot.factor* plot.formula* plot.function
[16] plot.hclust* plot.histogram* plot.isoreg*
[19] plot.lm plot.medpolish* plot.mlm
[22] plot.ppr* plot.prcomp* plot.princomp*
[25] plot.profile.nls* plot.spec plot.spec.coherency
[28] plot.spec.phase plot.stepfun plot.stl*
[31] plot.table* plot.ts plot.tskernel*
Functions declared in the global workspace are handled by patterns
on the name, since you can't declare things there: there's no
NAMESPACE file.
Non-visible functions are asterisked
Based on this, I think that methods("plot") should return
plot.function, so I am almost ready to take the bug word in my mouth.
When I debug the methods function it gets to the line
S3reg <- ls(get(".__S3MethodsTable__.", envir = defenv), pattern
= name)
where it searches the .__S3MethodsTable__. object. Consulting the
help page it seems that this object is part of the namespace
functionality.
My guess is that something goes wrong because function is a
reserved word?
I don't think so.
Duncan Murdoch
Kasper
This has been tested under R-2.7.1 on Mac OS X and under a not too
recent version of R-devel under x86_64. My sessionInfo for the Mac
version is
> sessionInfo()
R version 2.7.1 (2008-06-23)
i386-apple-darwin8.10.1
locale:
en_US.UTF-8/en_US.UTF-8/C/C/en_US.UTF-8/en_US.UTF-8
attached base packages:
[1] stats graphics grDevices utils datasets methods base
loaded via a namespace (and not attached):
[1] tools_2.7.1
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