Hello,
I would like to add a counter column in a data frame based on a set of
identical rows. To do this, I tested:
DF = data.table(x=c("a","a","a","b","c","d","e","f","f"),
y=c(1,3,2,8,8,4,NA,NA,NA))
DF[ , Index := .GRP, by = c("y") ]
DF
However, the rows with NAs are considered to be identical.
So, how can I obtain:
x y Index
1: a 1 1
2: a 3 2
3: a 2 3
4: b 8 4
5: c 8 4
6: d 4 5
7: e NA 6
8: f NA 7
9: f NA 8
Instead of:
x y Index
1: a 1 1
2: a 3 2
3: a 2 3
4: b 8 4
5: c 8 4
6: d 4 5
7: e NA 6
8: f NA 6
9: f NA 6
Thank you very much for your time.
Have a nice day
Marine
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