Re: [R] getting variable names from formula

[Douglas Bates]

Daniel Almirall wrote:
R-list,
1.  Given a formula (f) w variables referencing some data set (dat), is
there any easier/faster way than this to get the names (in character form)
of the variables on the RHS of '~' ?
 dat - data.frame(x1 = x1 - rnorm(100,0,1), x2 = x2 - rnorm(100,0,1), y = x1 
+ x2 + rnorm(100,0,1))
 f - y ~ x1 + x2
 mf - model.frame(f, data=dat)
 mt - attr(mf, terms)
 predvarnames - attr(mt, term.labels)

predvarnames
[1] x1 x2
-
2.  Also, is there an easy/fast way to do it, without having the data set
(dat) available?  That is, not using 'model.frame' which requires 'data'?
I understand that one approach for this is to use the way formulas are
stored as 'list's.  For example, this works
 predvarnames - character()
 for (i in 2:length(f[[3]]) ){
 predvarnames - c(predvarnames, as.character(f[[3]][[i]]))
 }

predvarnames
[1] x1 x2
but is there a better way?
Thanks,
Danny
__
R-help@stat.math.ethz.ch mailing list
https://stat.ethz.ch/mailman/listinfo/r-help
PLEASE do read the posting guide! http://www.R-project.org/posting-guide.html
That's exactly what the all.vars function does.  If you apply it to the 
formula you get all the names of variables referenced in the formula. 
If you only want the right hand side then apply it to the third 
component of the formula

 f - y ~ x1 + x2
 all.vars(f)
[1] y  x1 x2
 all.vars(f[[3]])
[1] x1 x2
__
R-help@stat.math.ethz.ch mailing list
https://stat.ethz.ch/mailman/listinfo/r-help
PLEASE do read the posting guide! http://www.R-project.org/posting-guide.html

Re: [R] getting variable names from formula

[Dimitris Rizopoulos]

maybe something like:
f - y ~ x1 + x2
attr(terms(f), term.labels)
but this wan't work if you have a more complex formula (e.g., f - y ~ 
x1*x2 + I(x1^2)) and you want only c(x1, x2).

I hope it helps.
Best,
Dimitris

Dimitris Rizopoulos
Ph.D. Student
Biostatistical Centre
School of Public Health
Catholic University of Leuven
Address: Kapucijnenvoer 35, Leuven, Belgium
Tel: +32/16/336899
Fax: +32/16/337015
Web: http://www.med.kuleuven.ac.be/biostat
http://www.student.kuleuven.ac.be/~m0390867/dimitris.htm
- Original Message - 
From: Daniel Almirall [EMAIL PROTECTED]
To: r-help@stat.math.ethz.ch
Sent: Tuesday, January 11, 2005 9:55 PM
Subject: [R] getting variable names from formula


R-list,
1.  Given a formula (f) w variables referencing some data set (dat), 
is
there any easier/faster way than this to get the names (in character 
form)
of the variables on the RHS of '~' ?

dat - data.frame(x1 = x1 - rnorm(100,0,1), x2 = x2 - 
rnorm(100,0,1), y = x1 + x2 + rnorm(100,0,1))

f - y ~ x1 + x2
mf - model.frame(f, data=dat)
mt - attr(mf, terms)
predvarnames - attr(mt, term.labels)
predvarnames
[1] x1 x2
-
2.  Also, is there an easy/fast way to do it, without having the 
data set
(dat) available?  That is, not using 'model.frame' which requires 
'data'?
I understand that one approach for this is to use the way formulas 
are
stored as 'list's.  For example, this works

predvarnames - character()
for (i in 2:length(f[[3]]) ){
predvarnames - c(predvarnames, as.character(f[[3]][[i]]))
}
predvarnames
[1] x1 x2
but is there a better way?
Thanks,
Danny
__
R-help@stat.math.ethz.ch mailing list
https://stat.ethz.ch/mailman/listinfo/r-help
PLEASE do read the posting guide! 
http://www.R-project.org/posting-guide.html

__
R-help@stat.math.ethz.ch mailing list
https://stat.ethz.ch/mailman/listinfo/r-help
PLEASE do read the posting guide! http://www.R-project.org/posting-guide.html