Hello Everyone-
I'm calculating summary statistics on a dataset (~4000 records, 
observations are not uniformly distributed) using summaryBy and trying 
to add a column with the number of observations to the output as well. 
What occurs to me is to use nrow(), but this doesn't appear to be working

I'm able to replicate the same results with an example from the 
summaryBy docs:

data(dietox)
dietox12<- subset(dietox,Time==12)
library(doBy)
#this one works
summaryBy(Weight+Feed~Evit+Cu,data=dietox12,FUN=c(mean,var,length))
#adding nrow doesn't give the number of rows
summaryBy(Weight+Feed~Evit+Cu,data=dietox12,FUN=c(mean,var,length,nrow))


There must be a way to do this, but I can't figure it out. I suspect 
there is another function that would be compatible with summaryBy.

Thanks in advance.
-Tony




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