R help - Oct 2009 - 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]

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]?

Thanks
-- 
View this message in context:
http://www.nabble.com/Using-a-variable-in-the-formula-tp26071598p26071598.html
Sent from the R help mailing list archive at Nabble.com.

On 27/10/2009, at 4:26 PM, jmark17 wrote:
>
> 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

######################################################################
Attention:\ This e-mail message is privileged and confid...{{dropped:9}}