update.lm question
On 15/11/2009 9:23 AM, Karsten Weinert wrote:
Hello,
at the Rgui command line I can easily remove a term from a fitted lm
object, like
fit <- lm(y~x1+x2+x3, data=myData)
update(fit, .~.-x1)
However, I would like to do this in a function with term given as string, like
removeTerm <- function(linModel, termName) { ??? }
removeTerm(fit, "x1")
but I can not fill the ???. I already tried
removeTerm <- function(linModel, termName) { update(linModel, .~. - termName },
removeTerm <- function(linModel, termName) { update(linModel, .~. -
as.name(termName) },
removeTerm <- function(linModel, termName) { update(linModel, .~. -
eval(termName) },
removeTerm <- function(linModel, termName) { update(linModel, .~. -
eval.parent(termName) },
removeTerm <- function(linModel, termName) { update(linModel, .~. -
get(termName) },
but these attempts produce error messages.
Can you advise me here?
There are two problems:
1. ".~." is different from ". ~ .".
2. You need to construct the formula ". ~ . - x1", and none of your
expressions do that. You need to use substitute() or bquote() to edit a
formula. For example, I think both of these should work:
removeTerm <- function(linModel, termName)
update(linModel, bquote(. ~ . - .(as.name(termName))))
removeTerm <- function(linModel, termName)
update(linModel, substitute(. ~ . - x, list(x=as.name(termName))))
Duncan Murdoch