[R] function to transform response of a formula

From: Paul Emberson <email_at_calidasoft.co.uk>
Date: Wed, 30 Jul 2008 10:50:26 +0100


Hi,

I am trying to write a function which takes a formula as input and outputs a new formula with a different response while keeping the rest of the formula the same.

I.e.

respapply : ( y ~ a+b ) -> ( f(y) ~ a + b )

I have tried the following but it doesn't work. The terms become invalid as shown below.

respapply <- function(fm, f) {

     fm[[2]] <- f(eval(fm[[2]]))
     fm;

}

> fm <- formula(y ~ a + b)
> y <- runif(5)
> newfm <- respapply(fm,identity)
> newfm

c(0.552921097259969, 0.939932722365484, 0.62522904924117, 0.899310540175065,
0.877736972644925) ~ a + b

> terms(newfm)

Error in terms.formula(fmapply(fm, identity)) :

   invalid term in model formula

Could someone put me in the right direction of how to correctly write a respapply function as described.

Regards,

Paul Emberson



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