[Rd] further notes on model.frame issue

[Charles C. Berry]

On Mon, 19 Jan 2009, Terry Therneau wrote:

> This is a follow-up on my note of Saturday.  Let me start with two important
> clarifications
>    - I think this would be a nice addition, but I've had exactly one use for it
> in the 15+ years of developing the survival package.
>    - I have a work around for the current case.
> Prioritize accordingly.
>
> The ideal would be to change survexp as follows:
>    fit <- survexp( ~ gender, data=mydata, ratetable=survexp.us,
>    	ratevar=list(sex=gender, year=enroll.dt, age=age*365.25))
>
> The model statement says that I want separate curves by gender, and is similar
> to other model statements.
>
> The ratevar option gives the mapping between my variable names and the dimnames
> of the survexp.us rate table.  It wants age in days, enrollment date to be some
> sort of date object, and sex to be a factor.  Then the heading of the R code
> would be
> 	m <- match.call()
> 	m <- m[c(1, match(names(m), c('data','formula','na.action', 'subset',
> 		                      'weights', 'ratevar'), nomatch=0)
>        m[[1]] <- as.name('model.frame')
>        m <- eval.parent(m)
>

Maybe I am missing something. Why not do something like this?

ratetable <- cbind ## for illustration purposes

foo <- function(formula,ratevars,data,...){
   m <- match.call()
   mfun <- m$ratevars
   mfun[[1]] <- as.name('ratetable')
   m$ratevars <- NULL
   frm <- eval(m$formula)
   frm <- update(frm,as.formula( paste("~.+",deparse(substitute(mfun)))))
   m$formula <- frm
   m[[1]] <- as.name('model.frame')
   m <- eval(m,parent.frame())
   m ## to show that model frame obeys
}

dat <- data.frame(diag(4))
foo(~X1+X2,list(sex=X3,year=X4),dat)

HTH,

Chuck

> That is, the variables enroll.dat and age are searched for in the data= arg.
> This is like the start opion in glm, but a more complex result than a vector.
>
>  The model.frame function can't handle this.  (Splus fails too, same spot, less
> useful error message).
>
> -----
>
>  The current code uses
>  	fit <- survexp(~ gender + ratetable(sex=gender, year=enroll.dt,
> age=age*365.25),
>  	      data=mydata, ratetable=survexp.us)
>
> The ratetable function creates a matrix with extra attributes. The matrix
> contains as.numeric of the factors with the levels remembered as an extra
> attribute, and also looks out for dates.  So the result is like ns() in the eyes
> of model.frame, and it works.  But having to write gender twice on the rhs is
> confusing to users.
>
>    Thanks in advance for any comments.
>
>    	Terry Therneau
>
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>

Charles C. Berry                            (858) 534-2098
                                             Dept of Family/Preventive Medicine
E mailto:cberry at tajo.ucsd.edu	            UC San Diego
http://famprevmed.ucsd.edu/faculty/cberry/  La Jolla, San Diego 92093-0901