[Rd] eval() bug in plot.formula() ?

[Peter Dalgaard BSA]

Martin Maechler <maechler@stat.math.ethz.ch> writes:

> I don't have time now to investigate myself,
> and I'm not feeling like deciding myself if the following is a bug:
> 
>   myplot <- function(dat, cex = 1.2, ...) {
>       if(!is.data.frame(dat <- as.data.frame(dat)))
> 	  stop("`dat' must be a data.frame")
>       if(any(is.na(match(c("x","y"), names(dat)))))
> 	  stop("`dat' must have a `x' and a `y' component")
>       plot(y ~ x, data= dat, cex=cex, ...)
>   }
> 
>   dd <- list(x= 1:12, y = sin((1:12)/10))
>   myplot(dd)
>   ## Error in eval(expr, envir, enclos) : ... used in an incorrect context
> 
>   myplot(dd, col = "red") ## Works fine
> 
>   myplot(dd, cex=1)
>   ## Error in eval(expr, envir, enclos) : ... used in an incorrect context
> 
> ------------
> The above code works fine in R 0.90  but fails already in 1.0.0
> 
> I believe it *is* a bug

Hmm, it comes from fixing a much worse bug (the one where pch and
friends didn't get subsetted), so it's not advisable to revert the
change.

The problematic construction is this:

{
    m <- match.call(expand.dots = FALSE)
    if (is.matrix(eval(m$data, parent.frame()))) 
        m$data <- as.data.frame(data)
    dots <- m$"..."
    dots <- lapply(dots, eval, data, parent.frame())

and the problem is that dots has ... as a component in some cases.
This looks more like a bug in match.call than in plot.formula, I think

-- 
   O__  ---- Peter Dalgaard             Blegdamsvej 3  
  c/ /'_ --- Dept. of Biostatistics     2200 Cph. N   
 (*) \(*) -- University of Copenhagen   Denmark      Ph: (+45) 35327918
~~~~~~~~~~ - (p.dalgaard@biostat.ku.dk)             FAX: (+45) 35327907
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