Hi, You have not given us all the data needed to reproduce your analysis (what is SectionF?), but the issue is probably that lm.r is a list and you're not treating it that way. Try
srt(lm.r) and summary(lm.r[[1]]) You may also want to look at the the lmList() function in the lme4 package. -Ista On Thu, Nov 12, 2009 at 8:26 PM, Sam Albers <tonightstheni...@gmail.com> wrote: > Hello R list, > > This is a question for anyone who has used the by() command. I would like to > perform a regression on a data frame by several factors. Using by() I think > that I have able to perform this using the following: > >> lm.r <- by(master, list(Sectionf=Sectionf, startd=startd), function(x) lm > (tot.c ~ starttime, data = x)) > > So that is, I would like to perform separate regressions for each level of > Sectionf for each level of startd. Now I can get the coefficients and > intercepts from all the fitted models. However, I am now unsure how to glean > more information from the regressions. If I follow up with this command I > get this: > >> summary(lm.r) > 9-09-04.Length 9-09-04.Class 9-09-04.Mode > 12 lm list > 12 lm list > 12 lm list > 9-09-11.Length 9-09-11.Class 9-09-11.Mode > 12 lm list > 12 lm list > 12 lm list > > Under normal circumstances, this usually ends up giving me more info about > the fitted model, but some reason when using the by() command it doesn't. > Similarly, although I wasn't hopeful that this would work, when I tried to > examine the residuals, I get these warning messages: > >> plot(lm.r$fit,lm.r$res,xlab="Fitted",ylab="Residuals") > Error in plot.window(...) : need finite 'xlim' values > In addition: Warning messages: > 1: In min(x) : no non-missing arguments to min; returning Inf > 2: In max(x) : no non-missing arguments to max; returning -Inf > 3: In min(x) : no non-missing arguments to min; returning Inf > 4: In max(x) : no non-missing arguments to max; returning -Inf > > So my question might be answered by someone saying that this isn't a good > way to do this. Still, can anyone suggest some strategies that might help me > out here? Specifically, how might I be able work with these regressions once > I have fitted all the models. Obviously I need to examine the residuals, > look at the model fit, etc. Any suggestions on what I might be doing wrong > would be much appreciated. I am also including a subset of the data and the > commands I used in case that is helpful. > > I am using Ubuntu 9.04 and R 2.8.1 > > Thanks in advance! > > Sam > >> attach(master) >> Sectionf <- factor(Section) >> startd=as.Date(startdate, format="%d/%m/%Y") > >> lm.r <- by(master, list(Sectionf=Sectionf, startd=startd), function(x) lm > (tot.c ~ starttime, data = x)) > > Data: > > "Section","starttime","startdate","tot.c" > "Upstream",0,04/09/09,0.17 > "Upstream",0,04/09/09,0.19 > "Upstream",0,04/09/09,0.14 > "Middle",0,04/09/09,0.2 > "Middle",0,04/09/09,0.13 > "Middle",0,04/09/09,0.11 > "Downstream",0,04/09/09,0.16 > "Downstream",0,04/09/09,0.17 > "Downstream",0,04/09/09,0.17 > "Upstream",25,04/09/09,0.17 > "Upstream",25,04/09/09,0.19 > "Upstream",25,04/09/09,0.14 > "Middle",25,04/09/09,0.2 > "Middle",25,04/09/09,0.13 > "Middle",25,04/09/09,0.11 > "Downstream",25,04/09/09,0.16 > "Downstream",25,04/09/09,0.17 > "Downstream",25,04/09/09,0.17 > "Upstream",50.06,04/09/09,0.17 > "Upstream",50.06,04/09/09,0.19 > "Upstream",50.06,04/09/09,0.14 > "Middle",50.06,04/09/09,0.2 > "Middle",50.06,04/09/09,0.13 > "Middle",50.06,04/09/09,0.11 > "Downstream",50.06,04/09/09,0.16 > "Downstream",50.06,04/09/09,0.17 > "Downstream",50.06,04/09/09,0.17 > "Upstream",75.42,04/09/09,0.17 > "Upstream",75.42,04/09/09,0.19 > "Upstream",75.42,04/09/09,0.14 > "Middle",75.42,04/09/09,0.2 > "Middle",75.42,04/09/09,0.13 > "Middle",75.42,04/09/09,0.11 > "Downstream",75.42,04/09/09,0.16 > "Downstream",75.42,04/09/09,0.17 > "Downstream",75.42,04/09/09,0.17 > "Upstream",100.14,04/09/09,0.17 > "Upstream",100.14,04/09/09,0.19 > "Upstream",100.14,04/09/09,0.14 > "Middle",100.14,04/09/09,0.2 > "Middle",100.14,04/09/09,0.13 > "Middle",100.14,04/09/09,0.11 > "Downstream",100.14,04/09/09,0.16 > "Downstream",100.14,04/09/09,0.17 > "Downstream",100.14,04/09/09,0.17 > "Upstream",125.31,04/09/09,0.17 > "Upstream",125.31,04/09/09,0.19 > "Upstream",125.31,04/09/09,0.14 > "Middle",125.31,04/09/09,0.2 > "Middle",125.31,04/09/09,0.13 > "Middle",125.31,04/09/09,0.11 > "Downstream",125.31,04/09/09,0.16 > "Downstream",125.31,04/09/09,0.17 > "Downstream",125.31,04/09/09,0.17 > "Upstream",150.29,04/09/09,0.17 > "Upstream",150.29,04/09/09,0.19 > "Upstream",150.29,04/09/09,0.14 > "Middle",150.29,04/09/09,0.2 > "Middle",150.29,04/09/09,0.13 > "Middle",150.29,04/09/09,0.11 > "Downstream",150.29,04/09/09,0.16 > "Downstream",150.29,04/09/09,0.17 > "Downstream",150.29,04/09/09,0.17 > "Upstream",0,11/09/09,0.12 > "Upstream",0,11/09/09,0.16 > "Upstream",0,11/09/09,0.12 > "Middle",0,11/09/09,0.08 > "Middle",0,11/09/09,0.12 > "Middle",0,11/09/09,0.1 > "Downstream",0,11/09/09,0.11 > "Downstream",0,11/09/09,0.13 > "Downstream",0,11/09/09,0.13 > "Upstream",25,11/09/09,0.12 > "Upstream",25,11/09/09,0.16 > "Upstream",25,11/09/09,0.12 > "Middle",25,11/09/09,0.08 > "Middle",25,11/09/09,0.12 > "Middle",25,11/09/09,0.1 > "Downstream",25,11/09/09,0.11 > "Downstream",25,11/09/09,0.13 > "Downstream",25,11/09/09,0.13 > "Upstream",50,11/09/09,0.12 > "Upstream",50,11/09/09,0.16 > "Upstream",50,11/09/09,0.12 > "Middle",50,11/09/09,0.08 > "Middle",50,11/09/09,0.12 > "Middle",50,11/09/09,0.1 > "Downstream",50,11/09/09,0.11 > "Downstream",50,11/09/09,0.13 > "Downstream",50,11/09/09,0.13 > "Upstream",75,11/09/09,0.12 > "Upstream",75,11/09/09,0.16 > "Upstream",75,11/09/09,0.12 > "Middle",75,11/09/09,0.08 > "Middle",75,11/09/09,0.12 > "Middle",75,11/09/09,0.1 > "Downstream",75,11/09/09,0.11 > "Downstream",75,11/09/09,0.13 > "Downstream",75,11/09/09,0.13 > "Upstream",100,11/09/09,0.12 > "Upstream",100,11/09/09,0.16 > "Upstream",100,11/09/09,0.12 > "Middle",100,11/09/09,0.08 > "Middle",100,11/09/09,0.12 > "Middle",100,11/09/09,0.1 > "Downstream",100,11/09/09,0.11 > "Downstream",100,11/09/09,0.13 > "Downstream",100,11/09/09,0.13 > "Upstream",125.04,11/09/09,0.12 > "Upstream",125.04,11/09/09,0.16 > "Upstream",125.04,11/09/09,0.12 > "Middle",125.04,11/09/09,0.08 > "Middle",125.04,11/09/09,0.12 > "Middle",125.04,11/09/09,0.1 > "Downstream",125.04,11/09/09,0.11 > "Downstream",125.04,11/09/09,0.13 > "Downstream",125.04,11/09/09,0.13 > > > > > > > -- > ***************************************************** > Sam Albers > Geography Program > University of Northern British Columbia > 3333 University Way > Prince George, British Columbia > Canada, V2N 4Z9 > phone: 250 960-6777 > ***************************************************** > > [[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. > -- Ista Zahn Graduate student University of Rochester Department of Clinical and Social Psychology http://yourpsyche.org ______________________________________________ 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.