[R] terms() and I( ) -- extract variables names only

[Thomas Lumley]

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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