[R] Environment of a formula

[Gabor Grothendieck]

Adrian Baddeley <adrian <at> maths.uwa.edu.au> writes:

: I want to equip a data frame with an attribute 
: which specifies how to plot some of the columns. 
: 
: Up to now we have been doing this by giving the data frame 
: a `formula' attribute, that can be passed to plot.formula.
: 
: For example
:       dat <- data.frame(x=1:100,y=runif(100),z=100:1)
:       attr(dat, "plotme") <- (z ~ x)
:       ......
:       ......
:       if(missing(desiredformula))
: 	desiredformula <- attr(dat, "plotme")
:       plot(desiredformula, data=dat)
: 
: We just got bitten by the fact that a formula object has a `.Environment'
: attribute, which may be huge, depending on the environment
: in which the formula was created. In the example above there is
: no upper limit on the size of the object 'dat' !!!!
: That is, environment(attr(dat, "plotme")) could be huge.

Do you mean that if fo is the formula then ls(environment(fo))
has many large components?   I don't understand why that would
be a problem.

: 
: What is the recommended/safe way to avoid this?
: I don't need the formula to have an environment at all; I'm just using
: the formula structure to represent the format of the plot.
: 
: It appears that we can't set the environment to NULL;
: should we set it to the Global environment e.g. using as.formula?

It works for me (R 2.1.0 Windows):

R> fo <- y~x
R> environment(fo)
<environment: R_GlobalEnv>
R> environment(fo) <- NULL
R> environment(fo)
NULL

: 
: Or is it wiser to save the formula as a character string 
: in the object 'dat' and only convert it back to a formula 
: at the last possible moment?