[R] A programming puzzler

Thomas Lumley tlumley at u.washington.edu
Mon Apr 9 01:57:48 CEST 2001

On Sat, 7 Apr 2001 fharrell at virginia.edu wrote:

> I am trying to replicate part of the function of the
> S-Plus terms.inner function.  I don't need an entire
> model terms object but R expressions or character
> strings containing the innermost variable name given
> a vector of character strings or expressions.  Here
> are some example inputs that each should result in the
> string or expression "x":
> x; x^2; g(x); h(g(x)); h(g(x^3)); j(h(g(pmin(x,3))))
> h(g(x)+g(y))
> To anyone who meets the challenge, thanks!

You're looking for all.vars(). It works on a formula, terms, or expression

> all.vars((~j(pmin(3,g(h(x^3*y))))))
[1] "x" "y"


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

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