[Rd] nlme: bug in getCovariateFormula (PR#1038)

[Douglas Bates]

Peter Dalgaard BSA <p.dalgaard@biostat.ku.dk> writes:

> Setzer.Woodrow@epamail.epa.gov writes:
> 
> > The final line in getCovariateFormula() in the nlme package (version
> > 3.1-16) is:
> >     eval(parse(text = paste("~", deparse(form))))
> > 
> > however, if deparse(form) exceeds 'width.cutoff (which defaults to 60)',
> > this results in inappropriately placed "~" signs:
> > For example, in my application with the error, form is
> > 
> > UnCompetitive(MethoxyresorufinConc, InhibitorConc, Vmax, Km, Ki)
> > 
> > the result of the paste() operation in the last line of getCovariateFormula
> > is:
> > 
> > > paste("~",deparse(form))
> > [1] "~ UnCompetitive(MethoxyresorufinConc, InhibitorConc, Vmax, Km, "
> > [2] "~     Ki)"
> > 
> > extending width.cutoff gives the intended value:
> > 
> > > paste("~",deparse(form,width.cutoff=500))
> > [1] "~ UnCompetitive(MethoxyresorufinConc, InhibitorConc, Vmax, Km, Ki)"
> > 
> > Seems a bit risky for an enforced cutoff in deparse, though.
> 
> parse(...deparse(...)) always looks wrong to me anyway. Couldn't one
> use something like
> 
> f <- ~1
> f[[2]] <- form
> eval(f)
> 
> or 
> 
> eval(as.call(list(as.name("~"),form)))

> or
> 
> eval(substitute(~form)) # that's not going to work in S, though...

Exactly.  The code was originally written for S and ported to R.  Some
of the contorted expressions were things that we found by
experimentation would work in both systems.

> ??
> 
> (What is the eval for? Doesn't usually do anything to a
> formula argument.)

In Sv3 at least it assigns a class to the object.

I'll change it to eval(substitute(~form)) for the R package.
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