[R] generating an expression for a formula automatically

[Gabor Grothendieck]

Use as.formula to convert the character string to an object of class "formula"
and note that we want to set the formula's environment appropriately:

fit.main <- function(resp, x, env = parent.frame()) {
	fo <- as.formula(paste("y", "~", paste(x, collapse = "+")))
	environment(fo) <- env
	fo
}

# test
fit.main("y", letters[1:3])


On 8/24/06, Maria Montez <montez at bu.edu> wrote:
> Hi!
>
> I would like to be able to create formulas automatically. For example, I
> want to be able to create a function that takes on two values: resp and
> x, and then creates the proper formula to regress resp on x.
>
> My code:
>
> fit.main <- function(resp,x) {
>  form <- expression(paste(resp," ~ ",paste(x,sep="",collapse=" + "),sep=""))
>  z <- lm(eval(form))
>  z
> }
> main <- fit.main("y",c("x1","x2","x3","x4"))
>
> and I get this error:
> Error in terms.default(formula, data = data) :
>        no terms component
>
> Any suggestions?
>
> Thanks, Maria
>
> ______________________________________________
> R-help at stat.math.ethz.ch mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.
>