[R] dynamic list in aggregate()

[William Dunlap]

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-bounces at r-project.org [mailto:r-help-bounces at r-project.org] On Behalf
> Of Xianming Wei
> Sent: Thursday, August 30, 2012 7:37 PM
> To: r-help at 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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