[R] update() ignores object

[Sverre Stausland]

Hi all,

I'm extracting the name of the term in a regression model that
dropterm specifies as the least significant one, and I'm assigning
this name to an object. However, when I use update(), it ignores this
object. Is there a way I can make it not ignore it? A reproducible
example is below:

> lm(x1~1+y1*y2+y3+y4,data=anscombe)->my.lm
> rownames(dropterm(my.lm,test="F",sort=TRUE))[1]->my.object
> my.object
[1] "y1:y2"
> update(my.lm,.~.-my.object)

Call:
lm(formula = x1 ~ y1 + y2 + y3 + y4 + y1:y2, data = anscombe)

Coefficients:
(Intercept)           y1           y2           y3           y4
   -8.95635      1.11420      0.61921      0.76762      0.21237
      y1:y2
   -0.04056

> update(my.lm,.~.-y1:y2)

Call:
lm(formula = x1 ~ y1 + y2 + y3 + y4, data = anscombe)

Coefficients:
(Intercept)           y1           y2           y3           y4
    -6.6409       0.7618       0.3836       0.7759       0.1640