Is this what you want?
> DAT
site obs frc
1 A 1.2745106 -1.6899502
2 B 1.4394225 0.4167296
3 A -0.1087532 0.7710872
4 B -0.6319814 -0.2177236
5 A -0.4208416 0.5099765
> (z <- by(DAT, list(DAT$site), function(x) mean(x$obs - x$frc)))
: A
[1] 0.3846007
------------------------------------------------------------------------------
: B
[1] 0.3042175
> cbind(z)
z
A 0.3846007
B 0.3042175
>
On Fri, Mar 21, 2008 at 4:15 PM, Matt Pocernich <[EMAIL PROTECTED]> wrote:
> Hello,
>
> I would like to use aggregate with a function that
> requires several argument that are columns of data.
>
> As a simple example, suppose I have data in the following dataframe and I
> would like to summarize the difference between columns obs and frc for each
> site. How would I do this? (In reality, the function is slightly more
> complicated, but still requires several columns of data.)
>
>
> > DAT <- data.frame(site = rep(c("A","B"), 10), obs = rnorm(20), frc =
> rnorm(20))
>
> > DAT
> site obs frc
> 1 A 1.27451057 -1.68995017
> 2 B 1.43942253 0.41672963
> 3 A -0.10875319 0.77108721
> 4 B -0.63198144 -0.21772356
> 5 A -0.42084163 0.50997647
> ....
>
> I have tried variations on the following syntax with no success.
>
> > F <- function(sub){
> mean(sub[,"obs"] - sub[,"frc"] )
> }
>
> > aggregate(DAT[,c("obs", "frc")], by = list(DAT$site), F)
>
>
> I have had partial success with the by command, but the by-class object is
> awkward and I would like to use the aggregate command to be consistent with
> other functions.
>
>
> Thanks,
>
> Matt
>
>
>
>
> --
> Matt Pocernich
> National Center for Atmospheric Research
> Research Applications Laboratory
> (303) 497-8312
>
> --
> Matt Pocernich
> National Center for Atmospheric Research
> Research Applications Laboratory
> (303) 497-8312
>
> ______________________________________________
> 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.
>
--
Jim Holtman
Cincinnati, OH
+1 513 646 9390
What is the problem you are trying to solve?
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