[R] Constructing groupedData objects in nlme - a little problem

[Hank Stevens]

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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Dr. Hank Stevens, Associate Professor
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