On Nov 15, 2009, at 11:15 AM, Karsten Weinert wrote:

Hello David,

of course I read those help pages and searched the r-help archive.

But did you look at the as.formula page?


I agree that the way should be clear, but I am stuck and looking for
help. Here is reproducible code

And here is what seemed like the obvious extension of your example but using as.formula:

myData <- data.frame(x1=rnorm(10), x2=rnorm(10), x3=rnorm(10), y=rnorm(10))
fit <- lm(y~x1+x2+x3, data=myData)
remvterm <- function(ft, termname) update(ft, as.formula(paste(".~.-", termname, sep="")))
remvterm(fit, "x3")

Call:
lm(formula = y ~ x1 + x2, data = myData)

Coefficients:
(Intercept)           x1           x2
    -0.2598      -0.0290      -0.2645

--
David



removeTerm1 <- function(linModel, termName) { update(linModel, .~. - termName) }
removeTerm2 <- function(linModel, termName) { update(linModel, .~. -
as.name(termName)) }
removeTerm3 <- function(linModel, termName) { update(linModel, .~. -
eval(termName)) }
removeTerm4 <- function(linModel, termName) { update(linModel, .~. -
eval.parent(termName)) }
removeTerm5 <- function(linModel, termName) { update(linModel, .~. -
get(termName)) }

myData <- data.frame(x1=rnorm(10), x2=rnorm(10), x3=rnorm(10), y=rnorm(10))
fit <- lm(y~x1+x2+x3, data=myData)

# all this does not work, as I am expecting the function to return a
lm object with formula y~x2+x3
removeTerm1(fit, "x1")
removeTerm2(fit, "x1")
removeTerm3(fit, "x1")
removeTerm4(fit, "x1")
removeTerm5(fit, "x1")


Any help appreciated,
kind regards,
Karsten Weinert



2009/11/15 David Winsemius <dwinsem...@comcast.net>:

You need to review:

?update
?update.formula
?as.formula

The way should be clear at that point. If not, then include a reproducible
data example to work with.

--
David

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David Winsemius, MD
Heritage Laboratories
West Hartford, CT

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