Message-ID: <94BA80DD-8731-4A13-8025-FA746697B9F9@auckland.ac.nz>
Date: 2009-10-27T04:24:48Z
From: Rolf Turner
Subject: Using a variable in the formula
In-Reply-To: <26071598.post@talk.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
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