Using a variable in the formula

I am sure this question has come up, but searching hasn't given me any
results.

So I need to enter this line:

mx1 <- randomForest(X1 ~ elevation + slope + vegtype, data =  
moths.train)

But the problem is that X1 is currently hard coded. I would instead  
like to
be able to put in the value of X1 through a list. For example:

list <- list("X1", "X2", "X3")
#Then, instead of X1, I want to put list[1]

No you don't.  You *might* want to put list[[1]] --- learn
	the difference between [[]] and [] for lists, i.e. RTFM, in
	particular ?"[" --- but it still wouldn't work.

mx1 <- randomForest(list[1] ~ elevation + slope + vegtype, data =
moths.train)

randomForest does not accept list[1] as a valid entry, so how can I  
get it
to accept it as X1, instead of list[1]?

(a) Don't call your list ``list''.  (Cf. fortune("dog").)

(b) You really want a character *vector* not a list.  E.g.

	nms <- c("X1", "X2", "X3")

(c) Execute

	fmla <- as.formula(paste(nms[1],"~ elevation + slope + vegtype"))
	mxl  <- randomForest(fmla,data=moths.train)

Have tested the construction of ``fmla'' --- that works.  I don't know
from randomForest(), so I haven't tested that bit.

HTH.

	cheers,

		Rolf Turner

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