[Rd] expand.model.frame fails when call creating model has no data (PR#1423)

[jfox@mcmaster.ca]

I've encounted a problem using expand.model.frame. To illustrate, consider 
the function

     > test <- function(model){
     +     expand.model.frame(model, "income")
     +     }
     >

The data frame Prestige (from the car library) has several variables, 
including prestige, income and education. I've attached this data frame and 
fit the following model

     > mod.1 <- lm(prestige ~ (log(income) + education)*type)
     >

 From the documentation for expand.model.frame, the default environment in 
which "things" are evaluated is environment(formula(model)), where model is 
the first argument to expand.model frame; in this case

     > environment(formula(mod.1))
     <environment: R_GlobalEnv>
     >

When I call the test function with mod.1, however, I get the following error:

     > test(mod.1)
     Error in eval(expr, envir, enclos) : Object "prestige" not found
     >

But if I fit the same model specifying the data argument to lm as Prestige, 
then test works,

     > mod.2 <- lm(prestige ~ (log(income) + education)*type, data=Prestige)
     > test(mod.2)
                             prestige log(income) education type income
     GOV.ADMINISTRATORS            68.8    9.421492     13.11 prof  12351
     GENERAL.MANAGERS              69.1   10.161187     12.26 prof  25879
     ACCOUNTANTS                   63.4    9.134647     12.77 prof   9271
     . . .
     TYPESETTERS                   42.2    8.773694     10.00   bc   6462
     BOOKBINDERS                   35.2    8.193400      8.55   bc   3617
     >

even though

     > environment(formula(mod.2))
     <environment: R_GlobalEnv>
     >

that is, still the global environment.


I'm able to get expand.model.frame to do what I think it's supposed to do 
by replacing the line

	rval <- eval(call("model.frame", ff, data = data, subset = subset,
             	na.action = I), envir)

with

         rval <- if (is.null(data)) eval(call("model.frame", ff, subset = 
subset, na.action = naa), envir)
            	else eval(call("model.frame", ff, data = data, subset = 
subset, na.action = naa), envir)


--please do not edit the information below--

Version:
  platform = i386-pc-mingw32
  arch = x86
  os = Win32
  system = x86, Win32
  status =
  major = 1
  minor = 4.1
  year = 2002
  month = 01
  day = 30
  language = R

Windows 2000 Professional (build 2195) Service Pack 2.0

Search Path:
  .GlobalEnv, Prestige, package:lattice, package:grid, package:car, 
package:ctest, Autoloads, package:base


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