[R] access to 'formula' terms in a user function

[Gabor Grothendieck]

Try this:


MyFunction <- function(formula, data) {
	vars <- all.vars(formula)
	data.name <- deparse(substitute(data))
	for(v in vars)
		cat("Mean of ", data.name, "$", v, ": ",
			mean(data[[v]]), "\n", sep = "")
	invisible(colMeans(data[vars]))
}
MyFunction(~ Sepal.Length + Petal.Length, iris)
out <- MyFunction(~ Sepal.Length + Petal.Length, iris)
out




On 7/6/07, Eric Peterson <peterson at heritage.nv.gov> wrote:
> This is probably buried somewhere in the R help archives, but I've been
> unable to find it, so perhaps the keywords I use here will help bring the
> topic to the surface more easily for future users.
>
> I want to write my own modeling function (ultimately for some
> multidimensional windowing - but this question is on scripting basics).  For
> purposes of figuring out my needs, lets just consider writing a function
> that takes a formula and a dataset, and outputs the mean of each variable in
> the formula model.  So:
>
> MyFunction <- function(AFormula, ADataFrame) {
>  ...
>  }
>
> >MyFunction(Y ~ A + B, TheData)
>
> would give results something like:
>
> Mean of MyData$Y is 5.3
> Mean of MyData$A is 3.4
> Mean of MyData$B is 8.2
>
> QUESTION 1:
> How do I determine the terms in the formula within the function?
>
> QUESTION 2:
> How do I use one of those terms to get to the individual columns, like
> MyData$Y ?
>
> Thanks!
> -Eric
> ---
> Eric Peterson
> Vegetation Ecologist
> Nevada Natural Heritage Program
>
>        [[alternative HTML version deleted]]
>
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