[R] seeking help with with()

[Peter Dalgaard BSA]

"Simon Fear" <Simon.Fear at synequanon.com> writes:

> I tried to define a function like:
> 
> fnx <- function(x, by.vars=Month)
>   print(by(x, by.vars, summary))
> 
> But this doesn't work (does not find x$Month; unlike other functions,
> such as
> subset(), the INDICES argument to "by" does not look for variables in
> dataset
> x. Is fully documented, but I forget every time). So I tried using
> "with":
> 
> fnxx <- function(x, by.vars=Month)
>   print(with(x, by(x, by.vars, summary)))
> 
> Still fails to find object x$Month. 
> 
> I DO have a working solution (below) - this post is just to ask: Can
> anyone
> explain what happened to the with()?
> 

Nothing, but by.vars is evaluated in the function frame where it is
not defined. I think you're looking for something like

function(x, by.vars) {
  if (missing(by.vars)) by.vars <- as.name("Month")
  print(eval.parent(substitute(with(x, by(x, by.vars, summary)))))
}

(Defining the default arg requires a bit of sneakiness...)
-- 
   O__  ---- Peter Dalgaard             Blegdamsvej 3  
  c/ /'_ --- Dept. of Biostatistics     2200 Cph. N   
 (*) \(*) -- University of Copenhagen   Denmark      Ph: (+45) 35327918
~~~~~~~~~~ - (p.dalgaard at biostat.ku.dk)             FAX: (+45) 35327907