access to 'formula' terms in a user function
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
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