On Aug 23, 2010, at 12:39 PM, Thaler, Thorn, LAUSANNE, Applied
Mathematics wrote:
Perfectly, works as expected. Regarding the other questions, can
anybody point me to the right direction?
So first question: where is the `+` operation defined for tables?
tables are a modification via attributes of matrices.
Is it
S4? How can I see the source code of S4 functions
I don't think so, at least from reading:
?Arithmetic
?groupGeneric
?InternalMethods
(I'm not very
comfortable with S4)? Or in general how do I find all generic
functions
for a specific class? I can get all S3 implementations of plot with
methods(plot), I can get all S4 functions with getMethods(plot). But
I've no idea of how to find all methods defined for a class? (e.g. all
functions that operate on tables, say)
Second question: my first dirty hack would be something like
args <- list(...)
table.sum <- args[[1]]
for (i in 2:length(args)) table.sum <- table.sum + args[[i]]
making use of the fact that `+` is defined for tables (and forgetting
about cases where two tables don't feature the same names). It works,
but isn't there a more elegant way to get the same?
Would sum() work better than "+"? The sum function is not a dyadic
operator.
(a <- table(rep(1:3, sample(10,3))))
k <- list(a,a,a)
> Reduce(sum, k )
[1] 51
> do.call("sum", k)
[1] 51
>
Last question: is there a way to determine the call stack, such that I
can see the names of the function which are actually executed when I
commit a command?
I know there is some feeling hereabouts that saying anything vaguely
like RTFM (of RTFA's) is passe, but I do believe that you can find
either the answer or pointers in the directions of an answer to this
by reviewing the posting over this last weekend to a question about
recovering from errors. (I was not the responder, so do not remember
the subject line. Oh heck. .... search, search, search, ... there it
is ... "on abort error, always show call stack?")
I know a little about R's dispatching mechanism for S3
classes (plot(a) actually calls plot.table) but I've no clue which
function is called if I type a + a (especially since `+` belongs to
the
generic function group Ops and I do not know at all whether its S4 or
S3). I read the documentation about S3 Group Generic Functions and
tried
to delve into S4,
Oh well. You've already been there. Maybe my advice above will help
someone else.
but obviously I was not able to understand everything
completely. So it would be great if somebody could help me out with
this
specific topic and point me to some resources where I can learn more.
Thanks for your help in advance.
BR,
Thorn
David Winsemius, MD
West Hartford, CT
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