[R] fixed effects

ivo welch ivowel at gmail.com
Tue Mar 28 04:29:11 CEST 2006

dear R wizards:

X is factor with 20,000*20=800,000 observations of 20,000 factors. 
I.e., each factor has 20 observations.  y is 800,000 normally
distributed data points.  I want to see how much R^2 the X factors can
provide.  Easy, right?

> lm ( y ~ X)
>  aov( y ~ X)
Error: cannot allocate vector of size 3125000 Kb

is this computationally infeasible?  (I am not an expert, but
off-hand, I thought this can work as long as the X's are just factors
= fitted means.)

> help.search("fixed.effects");

fixed.effects(nlme)                 Extract Fixed Effects
fixed.effects.lmList(nlme)          Extract lmList Fixed Effects
lme(nlme)                           Linear Mixed-Effects Models
lmeStruct(nlme)                     Linear Mixed-Effects Structure
nlme(nlme)                          Nonlinear Mixed-Effects Models
nlmeStruct(nlme)                    Nonlinear Mixed-Effects Structure

Type 'help(FOO, package = PKG)' to inspect entry 'FOO(PKG) TITLE'.

ok---I want to read the fixed.effects help.  could the help system
tell me how to inspect these entries?

> help("fixed.effects")
> help.search("fixed.effects")
two entries, as above.  nothing new.
> ?fixed.effects

eventually, it dawned on me that nlme in parens was not a function
argument, but the name of the package within which fixed.effects
lives.  Suggestion:  maybe a different notation to name packages would
be more intuitive in the help system.  yes, I know it now, but other
novices may not.  even a colon instead of a () may be more intuitive
in this context.

> library(nlme); ?lme
and then
> lme(y ~ X)
Error in getGroups.data.frame(dataMix, groups) :
        Invalid formula for groups

now I have to beg for some help.  ok, blatant free-riding.  the lme
docs tells me it does the Laird and Ware model, but I do not know this
model.  the only two examples given at the end of the lme help file
seem to be similar to what I just specified.  so, how do I execute a
simple fixed-effects model?  (later, I may want to add a variable Z
that is a continuous random variable.)  could someone please give me
one quick example?  help is, as always, highly appreciated.


/ivo welch

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