[Rd] Puzzled by eval

[Duncan Murdoch]

On 06/11/2015 7:36 AM, Therneau, Terry M., Ph.D. wrote:
> I am currently puzzled by a seach path behavior.  I have a library of a dozen routines
> getlabs(), getssn(), getecg(), ... that interface to local repositories and pull back
> patient information.  All have a the first 6 arguments in common, and immediately call a
> second routine to do initial processing of these 6.  The functions "joe" and "fred" below
> capture the relevant portion of them.
>     My puzzle is this: the last test in the "test" file works fine if these routines are
> sourced and executed at the command line, it fails if the routines are bundled up and
> loaded as a library. That test is motivated by a user who called his data set "t", and
> ended up with a match to base:::t instead of his data, resulting in a strange error
> message out of model.frame  --- you can always count on the users!  (There are a few hundred.)
>      I'm attempting to be careful with envr and enclos arguments -- how does base end up
> earlier in the search path?   Perhaps this is clearly stated in the docs and just not
> clear to me?  A working solution to the dilemma is of course more than welcome.

I haven't followed through all the details in fred(), but I can answer 
the last question.  In package code, the search order is:

- the package environment
- the imports to the package (with base being an implicit import)
- the global environment and the rest of the search list.

In code sourced to the global environment, only the third of these is 
searched.  Since base is in the second one, it is found first in the 
package version.

Duncan Murdoch


>
> Terry Therneau
>
>
> code:
> joe <- function(id, data, subset, na.action, date1, date2, other.args) {
>       Call <- match.call()
>       if (!missing(data)) temp <- fred(Call)
>
>       temp
> }
>
> fred <- function(Call) {
>       # get a first copy of the id and date variables
>       index <- match(c("id", "date1", "date2"), names(Call), nomatch=0)
>       temp <- Call[c(1, index)]
>       temp[[1]] <- as.name("list")
>
>       pf <- parent.frame(2)  # the caller of the caller
>       data <- eval(Call$data, envir=pf)
>
>       ldata <- eval(temp, data, enclos= pf)
>       date1 <- ldata$date1
>       date2 <- ldata$date2
>
>       # Users are allowed great flexibility with dates.  Both can be given
>       # as length 1 parameters, both can be in the data set, or one could
>       # be in each place.  Call model.frame with a built up formula that
>       # includes the id and any dates of length greater than 1. This allows
>       # subset and na.action to be applied in the usual way.
>       index <- match(c("data", "subset", "na.action"), names(Call), nomatch=0)
>       temp <- Call[c(1, index)]
>       temp[[1]] <- as.name("model.frame")
>       tform <- "~ id"
>       if (length(date1) > 1 && is.name(Call$date1))
>           tform <- paste(tform, "+", as.character(Call$date1))
>       if (length(date2) > 1 && is.name(Call$date2))
>           tform <- paste(tform, "+", as.character(Call$date2))
>
>       tform <- as.formula(tform)
>       environment(tform) <- pf
>       temp$formula <- tform
>       mf <- eval(temp, enclos=pf)
>
>       # At this point the real routine has checks for legal dates, date1 <= date2, etc
>       #  It returns the tidied up id, date1, date2 vectors.
>       list(ldata=ldata, mf=mf)
> }
>
> test:
> library(puzzle)
> tdata <- data.frame(id=1:10,
>                       start=as.Date(paste0("1999/", 1:10, "/25")))
> xdate <- as.Date(paste0(2001:2010, "/03/10"))
>
> joe(id, tdata, date1= "2001/10/11", date2= xdate[2])
> joe(id, tdata, date1=start, date2=xdate)
>
> sqrt <- xdate
> cos <- tdata
>
> joe(id, cos, date1=start, date2=sqrt)
>
> DESCRIPTION:
> Title: A puzzle
> Priority: optional
> Package: puzzle
> Version: 1.1-1
> LazyLoad: Yes
> LazyData: Yes
> Authors at R: c(person(c("Terry", "M"), "Therneau",
>                       email="therneau.terry at mayo.edu",
>                   role=c("cre")))
> Description: What gives with my tests?
> License: GPL
>
> NAMESPACE:
> export("joe")
>
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