[R] formula parsing, using parts ...

[Uwe Ligges]

Russell Senior wrote:

> I am writing a little abstraction for a series of tests.  For example,
> I am running an anova and kruskal.test on a one-factor model.  That
> isn't a particular problem, I have an interface like:
> 
>  my.function <- function(model,data) {
>    print(deparse(substitute(data)))
>    a <- anova(lm(formula,data))
>    print(a)
>    if(a$"Pr(>F)"[1] < 0.05) {
>       pairwise.t.test(???)
>    }
>    b <- kruskal.test(formula,data)
>    print(b)
>    if ...
>  }
> 
> I want to run each test, then depending on the resulting p-value, run
> pairwise tests.  I am getting into trouble where I put the ??? above.
> The pairwise.t.test has a different interface, that seems to want me
> to dismember the formula into constituent parts to feed in.  The other
> alternative is to give my.function the constituent parts and let it
> build the model.  I haven't figured out how to do either one.  Can
> someone give me some pointers?
> 

See ?formula and its "See Also" Section on how to do formula 
manipulation. There's also an example on how to construct a formula.

Uwe Ligges