Dear all,
I want to update an lm (or glm) object by changing the response variable and I
want to do so inside a function. Doing the update outside
of a function is straight forward:
x <- 1:5
y <- c(1,2,3,3,6)
mm <- lm(y~x)
y2 <- c(1,3,3,4,6)
mm2<- update(mm, y2 ~ .)
But I want to make the update inside a function (where the new response
variable is declared
inside the function). If I do
foo <- function(mod){
y3 <- c(1,3,3,4,6)
update(mod, y3 ~ .)
}
Then I get
foo(mm)
Error in eval(expr, envir, enclos) : object 'y3' not found
(because y3 is not known in the global environment - I suppose). To fix this I
do
foo2 <- function(mod){
y3 <- c(1,3,3,4,6)
mod2 <- eval(getCall(mod))
update(mod2, y3 ~ .)
}
foo2(mm)
Call:
lm(formula = y3 ~ x)
Coefficients:
(Intercept) x
0.1 1.1
Question: Is this the "appropriate" way of making such a model "available" for
an update inside a function,
or is there a better way? I guess so - because:
If I change the model formula of my model and then invoke foo2 I get
mm3 <- update(mm,.~.-x)
> foo2(mm3)
Error in eval(expr, envir, enclos) : object 'y3' not found
This puzzles me. Question: can anyone help me clarify why this happens and what
I can do to fix it.
Thanks in advance
Søren
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