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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