Noobie question, regression across levels

Much thanks! This helped a lot. Another quick one:
In using the lmList function in the nlme package, is it possible to subset
my data according to the number of observations in each level? (ie. I
obviously want to include only those levels in which the observations are
of sufficient size for regression). What is the best way to exclude
factors of insufficient size? Can I do it inside the lmList function? I've
read the requisite help files etc. and two hours later am still confused.
Thanks in advance,
Allen

Don't know if you can do it directly in lmList, but:

splitdat <- split(mydata,splitfactor)
lengths <- sapply(splitdat,nrow)  ## NOT sapply(splitdat,length)
splitdat <- splitdat[lengths>minlength]
lmfun <- function(d) { lm(y~x,data=d) }
myLmList <- lapply(splitdat,lmfun) 

OR

lengths <- sapply(split(mydata,splitfactor),nrow)
badlevels <- levels(splitfactor)[lengths<minlength]
subdata <- subset(mydata,!splitfactor %in% badlevels)

  and then proceed with lmList

  of course, I didn't test any of this ...

 Ben Bolker

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