On Wed, 11 Aug 2010, David Winsemius wrote:
On Aug 11, 2010, at 6:03 PM, Jarrett Byrnes wrote:
I have formulae with coefficents that I would like to update. However, I
get some strange results. For example, see the following:
For the formula y ~ d+ 3*r+t
Did you really get meaningful results from that formula? Care to provide an
example? Maybe there is something more for me to learn.
I want to add a variable p, so
> update(y~d+0*r+t, .~.+p)
In formulas the "*" operator is an interaction creator. so you told R to make
0 + r + 0:r. Probably not what you thought you were doing. So what were you
trying to do anyway?
produces
y ~ d + t + p - 1
Which at least explains why you got the -1 (which in R formulas is that same
as +0).
If the coefficient is not 0, but rather, something else - say, 3,
What do you think you are accomplishing when you put a scalar coefficient in
the formula?
Maybe he wants
?I
??
Chuck
I get the following:
> update(y~d+3*r+t, .~.+p)
Error in terms.formula(tmp, simplify = TRUE) :
invalid model formula in ExtractVars
>
Is there a way to do this,
or a different call I should be trying?
What you should be doing depends on what you want to happen.
--
David Winsemius, MD
West Hartford, CT
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Charles C. Berry (858) 534-2098
Dept of Family/Preventive Medicine
E mailto:cbe...@tajo.ucsd.edu UC San Diego
http://famprevmed.ucsd.edu/faculty/cberry/ La Jolla, San Diego 92093-0901
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