[Rd] backquotes and term.labels

Therneau, Terry M., Ph.D. therneau at mayo.edu
Wed Mar 7 14:22:45 CET 2018

Thanks to Bill Dunlap for the clarification.  On follow-up it turns out that this will be 
an issue for many if not most of the routines in the survival package: a lot of them look 
at the terms structure and make use of the dimnames of attr(terms, 'factors'), which also 
keeps the unneeded backquotes.  Others use the term.labels attribute.  To dodge this I 
will need to create a fixterms() routine which I call at the top of every single routine 
in the library.

Is there a chance for a fix at a higher level?

Terry T.

On 03/05/2018 03:55 PM, William Dunlap wrote:
> I believe this has to do terms() making "term.labels" (hence the dimnames of "factors")
> with deparse(), so that the backquotes are included for non-syntactic names.  The backquotes
> are not in the column names of the input data.frame (nor model frame) so you get a mismatch
> when subscripting the data.frame or model.frame with elements of terms()$term.labels.
> I think you can avoid the problem by adding right after
>      ll <- attr(Terms, "term.labels")
> the line
>      ll <- gsub("^`|`$", "", ll)
> E.g.,
>  > d <- data.frame(check.names=FALSE, y=1/(1:5), `b$a$d`=sin(1:5)+2, `x y z`=cos(1:5)+2)
>  > Terms <- terms( y ~ log(`b$a$d`) + `x y z` )
>  > m <- model.frame(Terms, data=d)
>  > colnames(m)
> [1] "y"            "log(`b$a$d`)" "x y z"
>  > attr(Terms, "term.labels")
> [1] "log(`b$a$d`)" "`x y z`"
>  >   ll <- attr(Terms, "term.labels")
>  > gsub("^`|`$", "", ll)
> [1] "log(`b$a$d`)" "x y z"
> It is a bit of a mess.
> Bill Dunlap
> TIBCO Software
> wdunlap tibco.com <http://tibco.com>
> On Mon, Mar 5, 2018 at 12:55 PM, Therneau, Terry M., Ph.D. via R-devel 
> <r-devel at r-project.org <mailto:r-devel at r-project.org>> wrote:
>     A user reported a problem with the survdiff function and the use of variables that
>     contain a space.  Here is a simple example.  The same issue occurs in survfit for the
>     same reason.
>     lung2 <- lung
>     names(lung2)[1] <- "in st"   # old name is inst
>     survdiff(Surv(time, status) ~ `in st`, data=lung2)
>     Error in `[.data.frame`(m, ll) : undefined columns selected
>     In the body of the code the program want to send all of the right-hand side variables
>     forward to the strata() function.  The code looks more or less like this, where m is
>     the model frame
>        Terms <- terms(m)
>        index <- attr(Terms, "term.labels")
>        if (length(index) ==0)  X <- rep(1L, n)  # no coariates
>        else X <- strata(m[index])
>     For the variable with a space in the name the term.label is "`in st`", and the
>     subscript fails.
>     Is this intended behaviour or a bug?  The issue is that the name of this column in the
>     model frame does not have the backtics, while the terms structure does have them.
>     Terry T.
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