[Rd] termplot fails for composite non-factor terms (PR#828)

[john.maindonald@anu.edu.au]

I am running R 1.2.1 under Windows 98SE.

termplot() currently fails when there are composite terms, thus:
  > library(mass)
  > data(hills)
  > hills.lm <- lm(time ~ climb + poly(dist, 2), data = hills)
  > termplot(hills.lm)
  Hit <Return> to see next plot: 
  Error in eval(expr, envir, enclos) : Object "dist" not found

The call
  > termplot(hills.lm,data=hills)
does run without generating an error message, i.e. there is a 
problem with the default setting for the parameter 'data'. 
However the x-axis for the term poly(dist,2) is then incorrectly 
labelled as poly(dist,2), rather than dist
The label poly(dist,2) surely belongs as part of the y-axis label.

Here are suggested fixes

1. In the default parameters for the function call change
   data = model.frame(model)
to
   data = get(as.character(model$call$data))

[This does not work if the variable values are specified in the
function call.  It is not clear to me how to fix that.]

2. A few lines from the beginning, replace
    if (is.null(xlabs)) 
        xlabs <- nmt
    if (is.null(ylab)) 
        ylab <- substitute(link(foo), list(foo = formula(model)[[2]]))
with
   if (is.null(xlabs)) 
        xlabs <- unlist(lapply(cn,function(x)
        if(length(x)>1)as.character(x[[2]]) else as.character(x)))
   if (is.null(ylab)) 
        ylab <- paste("Partial for", nmt)

[The current y-label is "link(<yvar>)".  If it is thought necessary
to specify this, it should be additional to e.g., in my example,
"Partial for poly(dist,2)"]

Replace ylab = ylab with 
   ylab = ylab[i]
in the two places (arguments to plot()) where it appears.

John Maindonald               email : john.maindonald@anu.edu.au        
Statistical Consulting Unit,  phone : (6125)3998        
c/o CMA, SMS,                 fax   : (6125)5549  
John Dedman Mathematical Sciences Building
Australian National University
Canberra ACT 0200
Australia

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