On 03 Oct 2014, at 14:32 , Joris Meys <jorism...@gmail.com> wrote:
> Dear all,
>
> I'm updating a package regarding a new type of models, and I'm looking to
> extend the formula interface with two functions (L() and R() ) for
> construction of these models. I want to use as much of the formula
> interface as possible, and hoped to do something similarly to I().
>
> I know the I() function does nothing more than add the class "AsIs". I've
> been browsing the source code of R for a couple of days now trying to
> locate where this class assignment gets translated into a specific action,
> but i couldn't locate it. I've been as far as the internal C function
> modelframe.
>
> Any pointers on how I() is processed internally are greatly appreciated.
It isn't...
> E <- function(x)x
> x <- rnorm(10)
> y <- rnorm(10)
> lm(y~x+E(x^2))
Call:
lm(formula = y ~ x + E(x^2))
Coefficients:
(Intercept) x E(x^2)
0.2757 0.1725 -0.3823
The point is that special interpretation of operators never happens inside
function calls. I() is just a convenient do-nothing function call.
If you want to add special operators, one place to look is in the handling of
specials for survival::coxph.
>
> Cheers
> Joris
>
> --
> Joris Meys
> Statistical consultant
>
> Ghent University
> Faculty of Bioscience Engineering
> Department of Mathematical Modelling, Statistics and Bio-Informatics
>
> tel : +32 9 264 59 87
> joris.m...@ugent.be
> -------------------------------
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