help with eval()

On 11-04-18 5:51 PM, Terry Therneau wrote:

I've narrowed my scope problems with predict.coxph further.
Here is a condensed example:

fcall3<- as.formula("time ~ age")
dfun3<- function(dcall) {
     fit<- lm(dcall, data=lung, model=FALSE)
     model.frame(fit)
}
dfun3(fcall3)

The final call fails: it can't find 'dcall'.

The relevant code in model.frame.lm is:
        env<- environment(formula$terms)
        if (is.null(env))
             env<- parent.frame()
	eval(fcall, env, parent.frame())

If the environment of the formula is .Globalenv, as it is here, the
contents of parent.frame() are ignored.  Adding a
            print(ls(parent.frame()))
statement just above the  final call shows that it isn't a scope issue:
the variables we want are there.

   I don't understand the logic behind looking for variables in the place
the formula was first typed (this is not a complaint).  The inability to
look elsewhere however has stymied my efforts to fix the scoping problem
in predict.coxph, unless I drop the env(formula) argument alltogether.
But I assume there must be good reasons for it's inclusion and am
reluctant to do so.

The reason is that when a formula is created, the variables in it are assumed 
to have meaning in that context.  Where you work with the formula after that 
should not be relevant:  that's why formulas carry environments with them. 
When you create the formula before the variables, things go wrong.

There's probably a way to associate the lung dataframe with the formula, or 
create the formula in such a way that things work, but I can't spot it.

Duncan Murdoch

Terry Therneau

sessionInfo()

R version 2.13.0 RC (2011-04-12 r55424)
Platform: x86_64-unknown-linux-gnu (64-bit)

locale:
  [1] LC_CTYPE=en_US.UTF-8       LC_NUMERIC=C
  [3] LC_TIME=en_US.UTF-8        LC_COLLATE=C
  [5] LC_MONETARY=C              LC_MESSAGES=en_US.UTF-8
  [7] LC_PAPER=en_US.UTF-8       LC_NAME=C
  [9] LC_ADDRESS=C               LC_TELEPHONE=C
[11] LC_MEASUREMENT=en_US.UTF-8 LC_IDENTIFICATION=C

attached base packages:
[1] stats     graphics  grDevices utils     datasets  methods
base

PS. This also fails
dfun3<- function(dcall) {
     fit<- lm(dcall, data=lung)
     model.frame(fit, subset=1:10)
}
You just need to force model.frame.lm to recreate data.