[R] dynamic list in aggregate()

[arun]

HI,

You can also use these in addition to aggregate:
tapply(dat$x,INDEX=dat[grp],mean)
library(plyr)
ddply(dat,.(dat[grp]$a,dat[grp]$d),summarize,mean(x))
#  dat[grp]$a dat[grp]$d         ..1
#1          b          c  0.26781378
#2          b          d -0.01994023
#3          c          e  0.14874737
#4          d          d -0.21051512
#5          e          b  0.18821072

A.K.



----- Original Message -----
From: Xianming Wei <XWei at bses.com.au>
To: "r-help at r-project.org" <r-help at r-project.org>
Cc: 
Sent: Thursday, August 30, 2012 10:37 PM
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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