[Rd] [.terms

[Roger Koenker]

This is a suggestion to modify the behavior of [.terms in base so that behaves as in
library(survival).  In my 1.7.0 (which is admittedly a couple of weeks old):

> tt <- terms(y~qss(x)+qss(z)+w,specials="qss")
> tt
y ~ qss(x) + qss(z) + w
attr(,"variables")
list(y, qss(x), qss(z), w)
attr(,"factors")
       qss(x) qss(z) w
y           0      0 0
qss(x)      1      0 0
qss(z)      0      1 0
w           0      0 1
attr(,"term.labels")
[1] "qss(x)" "qss(z)" "w"
attr(,"specials")
attr(,"specials")$qss
[1] 2 3

attr(,"order")
[1] 1 1 1
attr(,"intercept")
[1] 1
attr(,"response")
[1] 1
attr(,".Environment")
<environment: R_GlobalEnv>

With survival loaded you can do something like the following:

>  tmpc <- untangle.specials(tt,"qss")
> tmpc
$vars
[1] "qss(x)" "qss(z)"

$terms
[1] 1 2

> tt[-tmpc$terms]
y ~ w
attr(,"variables")
list(y, w)
attr(,"factors")
  w
y 0
w 1
attr(,"term.labels")
[1] "w"
attr(,"specials")
attr(,"specials")$qss
NULL

attr(,"order")
[1] 1
attr(,"intercept")
[1] 1
attr(,"response")
[1] 1
attr(,".Environment")
<environment: R_GlobalEnv>

This is rather handy for preprocessing additive nonparametric components of the formula
for example.  Without survival loaded [ operates on the formula not the terms object to
a much less satisfactory effect.

Thanks to Thomas Lumley for pointing out to me that survival had this capability...


url	www.econ.uiuc.edu	Roger Koenker		Dept. of Economics UCL,
email	rkoenker at uiuc.edu	Department of Economics Drayton House,
vox: 	217-333-4558		University of Illinois	30 Gorden St,
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