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2011 May 09
2
Creating Observation ID
If I have a data frame something like: Value=rnorm(30) Group = sample(c('A','B','C'), 30, replace=TRUE) df = data.frame(Value, Group) It seems like it should be simple to create an 'ObsID' column which indicates the observation order of each Value within each of the 3 groups. Somehow, I can't quite see how to do it without manually sub-setting the parent data