Perfectly clear. Thanks!
Best,
Wolfgang
On Sat, 13 Nov 2021, Duncan Murdoch wrote:
On 13/11/2021 2:24 p.m., Viechtbauer, Wolfgang (SP) wrote:
Hello all,
Say I would like to change the outcome in a formula to a variable not part
of the original dataset. This works just fine:
res <- lm(mpg ~ wt + cyl, data=mtcars)
res
y <- rnorm(nobs(x))
update(x, formula = y ~ .)
But not when doing so within a function:
rm(y)
f <- function(x) {
y <- rnorm(nobs(x))
update(x, formula = y ~ .)
}
f(res)
Is there a way to make this work? Using y <<- ... inside the function
works, but I would like to avoid such a heavy-handed approach.
Formulas have associated environments, and that's where functions using them
look for variables. update() leaves the formula environment unchanged, as
documented in ?update.formula. Since yours started out as globalenv(), you
would need to put y there, and that's what you want to avoid.
However, the default update() method (the one you call on res, that calls the
formula method) allows you to change other things.
So you could do it this way:
res <- lm(mpg ~ wt + cyl, data=mtcars)
f <- function(x) {
y <- rnorm(nobs(x))
newdata <- cbind(model.frame(x), y)
update(x, formula = y ~ ., data = newdata)
}
f(res)
Duncan Murdoch
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