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
*****************************************************
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