I'm working on getting this to work - need to figure out how to extract pieces properly.
In the mean time, I may have figured out an alternate method to group the factors by the following: > stems139$SpeciesF <- factor(stems139$Species) > stems139GLM <- glm(Stems ~ Time*SizeClassF*Species, family=poisson, data=stems139) > summary(stems139GLM) Call: glm(formula = Stems ~ Time * SizeClassF * Species, family = poisson, data = stems139) Deviance Residuals: Min1QMedian3QMax -4.2308-1.0107-0.6786-0.339316.7415 Coefficients: Estimate Std. Error z value Pr(>|z|) (Intercept)-0.6717940.118678-5.661 1.51e-08 *** TimeVTM-0.5738000.197698-2.902 0.003703 ** SizeClassF2-0.7661720.210684-3.637 0.000276 *** SizeClassF3-1.960095 0.337764-5.803 6.51e-09 *** SizeClassF4-2.6532420.462693-5.734 9.79e-09 *** SpeciesABMA1.8240950.12789514.262< 2e-16 *** SpeciesJUOC-0.0882930.171666-0.514 0.607022 SpeciesPIAL1.9479200.12685615.355 < 2e-16 *** SpeciesPICO2.8634070.12201823.467 < 2e-16 *** SpeciesPIJE-0.5250100.194664-2.697 0.006997 ** SpeciesPIMO0.3720490.1542512.412 0.015866 * SpeciesTSME1.9194050.12708515.103< 2e-16 *** TimeVTM:SizeClassF2-0.6201220.411567-1.507 0.131879 TimeVTM:SizeClassF30.7561220.4716121.603 0.108875 TimeVTM:SizeClassF40.9102730.6180141.473 0.140778 The problem now though, is that R for some reason does not list factor 1 in the output. Why would this be? On 2/8/2011 2:21 PM, Dennis Murphy wrote: > Hi: > > One approach would be to use dlply() from the plyr package to generate > the models and assign the results to a list, something like the following: > > library(plyr) > # function to run the GLM in each data subset - the argument is a > generic data subset d > gfun <- function(d) glm(Stems ~ Time, data = d, family = poisson) > mlist <- dlply(stems139, .(SizeClass, Species), gfun) > > To see the result, try mlist[[1]] or summary(mlist[[1]]) to execute > the print and summary methods on the first fitted model. Each output > list object from glm() is a list component of mlist, so mlist is > actually a list of lists. > > You can extract various pieces from mlist by using ldply() with a > suitable extraction function or by use of the do.call/lapply combination. > > All of this is untested since no minimal example was provided per > instructions in the Posting Guide... > > HTH, > Dennis > > > On Tue, Feb 8, 2011 at 11:54 AM, Christopher R. Dolanc > <crdol...@ucdavis.edu <mailto:crdol...@ucdavis.edu>> wrote: > > I'm having a hard time figuring out how to group results by > certain factors in R. I have data with the following headings: > > [1] "Time" "Plot" "LatCat" "Elevation" "ElevCat" > "Aspect" "AspCat" "Slope" > [9] "SlopeCat" "Species" "SizeClass" "Stems" > > and I'm trying to use a GLM to test differences in "Stems" for > different categories/factors - most importantly, I want to group > things so that I see results by "SizeClass" and then by "Species". > This is pretty easy in SAS using the "Group By" command, but in > R, I haven't figured it out. > > I've tried using the following code: > > > stems139GLM <- glm(Stems ~ Time | SizeClass | Species, > family=poisson, data=stems139) > > but R gives me this message: > > Error in pmax(exp(eta), .Machine$double.eps) : > cannot mix 0-length vectors with others > In addition: Warning messages: > 1: In Ops.factor(Time, SizeClass) : | not meaningful for factors > 2: In Ops.factor(Time | SizeClass, Species) : | not meaningful for > factors > > I'd appreciate any help. > > Thanks. > > -- > Christopher R. Dolanc > PhD Candidate > Ecology Graduate Group > University of California, Davis > Lab Phone: (530) 752-2644 (Barbour lab)un > > ______________________________________________ > R-help@r-project.org <mailto:R-help@r-project.org> mailing list > https://stat.ethz.ch/mailman/listinfo/r-help > PLEASE do read the posting guide > http://www.R-project.org/posting-guide.html > and provide commented, minimal, self-contained, reproducible code. > > -- Christopher R. Dolanc PhD Candidate Ecology Graduate Group University of California, Davis Lab Phone: (530) 752-2644 (Barbour lab) [[alternative HTML version deleted]] ______________________________________________ R-help@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code.
