[R] updating formula inside function

[Gabor Grothendieck]

This was just discussed last week:

https://www.stat.math.ethz.ch/pipermail/r-help/2006-January/083812.html

On 1/11/06, Christian Bieli <bieli at biomillaufen.ch> wrote:
> Dear R-Helpers
>
> Given a function like
> foo <- function(data,var1,var2,var3) {
>        f <- formula(paste(var1,'~',paste(var2,var3,sep='+'),sep=''))
>        linmod <- lm(f)
>        return(linmod)
> }
> By typing
> foo(mydata,'a','b','c')
> I get the result of the linear model a~b+c.
> How can I rewrite the function so that the formula can be updated inside
> the function, i.e.
> foo <- function(data,var1,var2,var3,var4) {
>        f <- formula(paste(var1,'~',paste(var2,var3,sep='+'),sep=''))
>        linmod <- lm(f)
>        return(linmod)
>        f2 <- update.formula(f,.~.-var3+var4)
> }
> Like that it won't work because var3 and var4 are characters, but also
> with substitute() and eval() I did not manage to get the favoured result.
> Can somebody help me out?
> Thank you in advance
>
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