R help - Dec 2000 - terms() and I( ) -- extract variables names only

Hi,

I am having difficulties extracting all variables used in a formula. Here's 
an example of what I am doing:
> my.formula <- v1 ~ v2 + v3 + I(v4/v5)
> out.terms <- terms(my.formula)
> paste(attr(out.terms, "variables"))[-1]
[1] "v1"       "v2"       "v3"      
"I(v4/v5)"

BUT what I would like to get is

[1] "v1"       "v2"       "v3"      
"v4"       "v5"

Also, if I change I(v4/v5) to I(v4^2) or any other expression, it should only 
extract the variable (here, V4).

Is there a built-in function to do it? Suggestions are extremely appreciated. 
Thank you for your attention,

Alvaro A. Novo
R-1.2.0
Linux SuSE 6.4
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On Thu, 21 Dec 2000, [iso-8859-1] Álvaro A. Novo wrote:
> Hi,
> 
> I am having difficulties extracting all variables used in a formula.
Here's
> an example of what I am doing:
> 
> > my.formula <- v1 ~ v2 + v3 + I(v4/v5)
> > out.terms <- terms(my.formula)
> > paste(attr(out.terms, "variables"))[-1]
> [1] "v1"       "v2"       "v3"      
"I(v4/v5)"
> 
> BUT what I would like to get is
> 
> [1] "v1"       "v2"       "v3"      
"v4"       "v5"
> 
> Also, if I change I(v4/v5) to I(v4^2) or any other expression, it should
only
> extract the variable (here, V4).
> 
> Is there a built-in function to do it? Suggestions are extremely
appreciated.
all.vars()

	-thomas
Thomas Lumley			Asst. Professor, Biostatistics
tlumley at u.washington.edu	University of Washington, Seattle

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