[R] Simple way to define a function to be used in a formula object inside another function

[William Dunlap]

The following works because model.frame looks for things in environment(formula)
and ancestral environments thereof.  It puts the new things in a child environment
of the original environment(formula) so it does not alter the original environment.

f2 <- function (formula, data = NULL) 
{
    environment(formula) <- new.env(parent = environment(formula))
    assign(envir = environment(formula), "gg", sqrt)
    model.frame(formula, data = data)
}

Bill Dunlap
Spotfire, TIBCO Software
wdunlap tibco.com

> -----Original Message-----
> From: r-help-bounces at r-project.org [mailto:r-help-bounces at r-project.org] On Behalf
> Of Frank Harrell
> Sent: Sunday, December 15, 2013 10:09 AM
> To: RHELP
> Subject: [R] Simple way to define a function to be used in a formula object inside another
> function
> 
> I would like to do this:
> 
> f <- function(formula, data=NULL) {
>   gg <- sqrt
>   model.frame(formula, data=data)
>   }
> x <- y <- 1:10
> f(y ~ gg(x))
> Error in eval(expr, envir, enclos) : could not find function "gg"
> 
> Is there a simple way to get access to gg from within the model.frame
> invocation inside f?
> 
> Thanks
> Frank
> 
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