I don't have any concerns about these changes, don't see any need to
preserve the old behaviour.
In lme4 and glmmTMB (and now broken out into a separate `reformulas`
package, I do this the hard way, walking down the parse trees of formula
objects and looking for specials, and not using the functionality here.
Mikael showed how I could use the *new* functionality instead:
https://github.com/bbolker/reformulas/issues/4
but honestly if I were going to change things in `reformulas` it would
be in the direction of streamlining and refactoring, not changing the
basic approach.
cheers
Ben Bolker
On 2025-04-14 5:43 p.m., Mikael Jagan wrote:
[CC: maintainers of R packages survival, mgcv, lme4, RItools]
Dear R-devel subscribers,
If you have never used stats:::terms.formula or its 'specials' argument,
then feel free to stop reading or otherwise review help("terms.formula")
and help("terms.object").
Folks may have noticed a recent change in R-devel:
$ svn log -v -r 88066
------------------------------------------------------------------------
r88066 | maechler | 2025-03-28 17:04:27 -0400 (Fri, 28 Mar 2025) |
1 line
Changed paths:
M /trunk/doc/NEWS.Rd
M /trunk/src/library/stats/src/model.c
M /trunk/tests/reg-tests-1e.R
terms(<formula>, specials = "<non-syntactic>") now works
------------------------------------------------------------------------
intended to resolve Bug 18568
https://bugs.r-project.org/show_bug.cgi?id=18568
which pointed out the following undesirable behaviour in R-release:
> attr(terms(~x1 + s (x2, f) + s (x3, g), specials = "s"),
"specials")
$s
[1] 2 3
> attr(terms(~x1 + `|`(x2, f) + `|`(x3, g), specials = "|"),
"specials")
$`|`
NULL
namely that non-syntactic names like "|" were not supported.
Unfortunately,
the patch (r88066) broke one package on CRAN, RItools, which relied on the
following
> attr(terms(~x1 + mgcv::s (x2, f), specials = "mgcv::s"),
"specials")
$`mgcv::s`
[1] 2
> attr(terms(~x1 + `mgcv::s`(x2, f), specials = "mgcv::s"),
"specials")
$`mgcv::s`
NULL
whereas in R-devel we see
> attr(terms(~x1 + mgcv::s (x2, f), specials = "mgcv::s"),
"specials")
$`mgcv::s`
NULL
> attr(terms(~x1 + `mgcv::s`(x2, f), specials = "mgcv::s"),
"specials")
$`mgcv::s`
[1] 2
A strict interpretation of 'specials' as a list of *name*s of functions
would
suggest that the old behaviour was "wrong" (and accidental, predating
package
namespaces altogether) and that the new behaviour is "right". After all,
`mgcv::s` (with backticks) is a name (of type "symbol", class "name")
whereas
mgcv::s (without backticks) is a call (of type "language", class "call").
Martin and I are requesting comments from the community, especially R-core
members and package authors who use 'specials', on the following:
1. Should the previous (long standing but undocumented, likely
rarely used)
behaviour be preserved going forward?
2. If we pursue a more *robust* implementation of namespace
resolution by
stats:::terms.formula, not relying on details of how non-
syntactic names
are deparsed, then what should that look like?
(I say "likely rarely used" because stats:::terms.formula is called
primarily by
package *authors* to parse formulas of package *users*. Only a subset
of those
packages will set 'specials', only a subset of *those* packages will set
specials="<pkg>::<name>", and only one such package is known to be
broken due
to r88066.)
Relevant to (2) is an earlier thread
https://stat.ethz.ch/pipermail/r-devel/2025-March/083906.html
in which I proposed that we make use of an optional 'package' attribute of
'specials', so that
specials = structure(c("s", "s"), package = c("", "mgcv"))
would match calls s(...) and mgcv::s(...) separately. This attribute
would be
preserved by the 'specials' component of the 'terms' object, e.g.,
> attr(terms(~x1 + s(x2, f) + mgcv::s(x3, g),
+ specials = structure(c("s", "s"), package = c("",
"mgcv"))),
+ "specials")
$s
[1] 2
$s
[1] 3
attr(,"package")
[1] "" "mgcv"
A patch against R-devel (at r88141) implementing this proposal is attached.
Mikael
--
Dr. Benjamin Bolker
Professor, Mathematics & Statistics and Biology, McMaster University
Director, School of Computational Science and Engineering
> E-mail is sent at my convenience; I don't expect replies outside of
working hours.
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