[Rd] problems with plot.formula

[Prof Brian Ripley]

As this happens in exactly the same way in 1.8.1 and 1.9.0, why are you
blaming `recent changes in R 1.9.x'?  I am baffled as to what you think is
`recent'.

On Tue, 25 May 2004, Warnes, Gregory R wrote:

> 
> With the recent changes in R 1.9.x, it is now impossible to properly call
> plot on a formula() where the formula is provided via a named first
> argument.  On today's R-1.9.1-alpha:
> 
> > x <- 1:10
> > y <- rnorm(x,0.25)
> > 
> > plot(x~y)
> > 
> > plot(x=x~y)
> Error in terms.formula(formula, data = data) : 
> 	argument is not a valid model
> > 
> > plot(formula=x~y)
> Error in plot(formula = x ~ y) : Argument "x" is missing, with no default
> > 
> 
> This occurs because plot.formula is no longer directly callable, 

It is, via graphics:::plot.formula.

> and the
> first argument to plot.formula() is 'formula' while the first argument to
> plot() is 'x'.   Consequently one cannot properly pass a named first
> argument since it will either fail for plot() or for plot.formula().  [I
> suspect this is one reason why R CMD check complains about S3 methods that
> don't match the call of the base method.]
> 
> This is much of a problem in interactive use, but it does cause problems in
> functions, like my gregmisc::overplot(), which use the standard idiom
> 
>     m <- match.call()
>     m[[1]] <- as.name('plot')
>     eval(m, parent.frame() )

Not a standard idiom for a generic with a formula method, and I think you 
really should be dispatching to the method here.

[...]

-- 
Brian D. Ripley,                  ripley at stats.ox.ac.uk
Professor of Applied Statistics,  http://www.stats.ox.ac.uk/~ripley/
University of Oxford,             Tel:  +44 1865 272861 (self)
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