I haven't seen an answer yet, so I'll give it a shot (below).
On 2011-07-29 01:37, Thaler, Thorn, LAUSANNE, Applied Mathematics wrote:
Dear all,
Quite often I have the situation that I've multiple response variables
and I create Linear Models for them in a function. The following code
illustrates my usual approach:
---------------8<---------------
set.seed(123)
dat<- data.frame(x = rep(rep(1:3, each = 3), 4), y = rep(1:3, 12))
dat$z1<- rnorm(36, dat$x + dat$y)
dat$z2<- rnorm(36, dat$x + 2*dat$y)
dat$z3<- rnorm(36, dat$x + 3*dat$y)
modelInFunction<- function(resp, expl, df) {
fo<- as.formula(paste(resp, paste(expl, collapse = " + "), sep = " ~
"))
lm(fo, data = df)
}
ex<- c("x", "y")
resp<- paste("z", 1:3, sep = "")
models<- lapply(resp, modelInFunction, expl = ex, df = dat)
---------------8<---------------
So far so good. But if I try to update any of the models afterwards, I
get an error:
---------------8<---------------
update(models[[1]], . ~ . )
Error in terms.formula(formula, data = data) :
'data' argument is of the wrong type
---------------8<---------------
In my opinion this happens, because the update function does not know
where to look for the data frame containing the original values.
True. You can call update() with 'evaluate = FALSE' to see that
it can't find 'df'. The particular form of the error is because
'df' is a function (and hence possibly not a good choice for a
variable name). Replacing your 'df' with 'dta' I get
update(models[[1]], . ~ .)
#Error in inherits(x, "data.frame") : object 'dta' not found
But ?update tells us that we can provide additional or changed
arguments to the call. So an easy fix is:
update(models[[1]], . ~ ., data = dat)
or
update(models[[1]], . ~ ., data = model.frame(models[[1]]))
Peter Ehlers
However, if I try
---------------8<---------------
model.frame(models[[1]])
---------------8<---------------
I get the right answer. Thus, I guess it has something to do with
different environments and I was wondering what the recommended way
would be to create an LM object within a function, which could be
processed outside this particular function in the usual way? Or is it
simply a bug in update?
Any help highly appreciated.
Thanks,
-Thorn
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