Hi Dieter,
I never really used groupedData objects at all. I can imagine that if
you become even more immersed in nlme and lattice, groupedData could
reduce your typing, and sometimes simplify your life, but it was not a
hurdle I chose willingly.
Hank
On Jun 4, 2008, at 1:15 PM, Dieter Menne wrote:
Toby Marthews <Toby.Marthews <at> lsce.ipsl.fr> writes:
Dear R-help,
I am trying to create groupedData objects using the nlme library. I'm
missing something basic, I know:
Here is the first example in ch.1 of Pinheiro & Bates (2000):
...
...but, as you can see, the coefficients I get at the end this time
are
completely different and I don't know why. Somehow, I am not
creating the
structure properly even though the formula and data values are all
correct.
Hank is right. On the other hand your well-defined query points to a
problem
using groupedData. I do a lot of my work with nlme and love it, but
I admit
that I only started to understand it after I totally stopped using
groupedData.
Which makes reading Pinheiro/Bates sometimes difficult, because many
examples
give the impression that these must be done with groupedData.
Everything can be
done by explicitly saying what should be analyzed in lme and
friends, there is
no need to rely on groupedData.
Note that in lme4 that partially re-designs nlme, there is no such
thing as
groupedData.
Dieter
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