[R] 'with' usage question

[Prof Brian Ripley]

Default arguments are evaluated in the function frame, not in the calling 
environment (nor in the same place as explicit arguments).

> Which to me reads that a with statement as above is equivalent to
>
> > attach(data) ; aov.SS1(y=Obs) ; detach(data)
>
> Or is that just wishful thinking??

The latter.


On Thu, 7 Oct 2004, RenE J.V. Bertin wrote:

> Hello,
> 
> I'm having a little argument with the 'with' function. I have 
> 
> 
> aov.SS1 <- function( y, indep=speed, fSnr=Subject, ... )
> {
> 	indep <- factor(speed)
> 	fSnr <- factor(fSnr)
>   ## ....
> }
> 
> and a dataframe containing speed, Subject, and a bunch of other columns. If I now do
> 
> > with( data, aov.SS1( y=Obs ) )
> 
> I get a message
> 
> Error in factor(indep) : Object "speed" not found
> 
> It seems that automatic argument initialisation doesn't work, as the only effectively valid call seems to be
> 
> > with( data, aov.SS1( y=Obs, indep=speed, fSnr=Subject ) )
> 
> whereas
> 
> > with( data, speed )
> 
> prints what one would expect (i.e. data$speed).
> 
> How come? From ?with, one learns that 
>      "... assignments within 'expr' take place in the constructed
>      environment and not in the user's workspace."
> 
> Which to me reads that a with statement as above is equivalent to
> 
> > attach(data) ; aov.SS1(y=Obs) ; detach(data)
> 
> Or is that just wishful thinking??
> 
> RenE
> 
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-- 
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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