Replace
lst <- paste('dat$', grp, sep='', collapse =',')
aggregate(dat$x, list(lst), mean)
with
aggregate(dat$x, dat[grp], mean)
The 'by' argument to aggregate should be a list
and data.frames (like dat and dat[grp]) are lists.
Bill Dunlap
Spotfire, TIBCO Software
wdunlap tibco.com
> -----Original Message-----
> From: r-help-boun...@r-project.org [mailto:r-help-boun...@r-project.org] On
> Behalf
> Of Xianming Wei
> Sent: Thursday, August 30, 2012 7:37 PM
> To: r-help@r-project.org
> Subject: [R] dynamic list in aggregate()
>
> Hi all,
>
> How can I have a dynamic list for different combinations of grouping factors
> in the
> following example? Thanks.
>
> dat <- data.frame(x=rnorm(100),
> a=sample(letters[1:5], replace = T),
> b=sample(letters[1:5], replace = T),
> c=sample(letters[1:5], replace = T),
> d=sample(letters[1:5], replace = T))
>
> ## define grouping factors
> grp <- c('a','d') # or any combination among a, b, c and d
> ## something like this for the list
> lst <- paste('dat$', grp, sep='', collapse =',')
> ## aggregate on the defined list
> aggregate(dat$x, list(lst), mean)
>
> Thanks.
>
> Regards,
> Xianming
>
>
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