data.table equivalent of tidyr::complete()

Question

tidyr::complete() adds rows to a data.frame for combinations of column values that are missing from the data. Example:

library(dply         


        

Answer 1

There might be a better answer out there, but this works:

dt[CJ(person=unique(dt$person), 
      observation_id=unique(dt$observation_id)),
   on=c('person','observation_id')]

Which gives:

   person observation_id value
1:      1              1     1
2:      2              1     1
3:      1              2    NA
4:      2              2     1

Now, if you would like to be able to fill with any value (and not NA), I would suggest to wait for the corresponding feature to be finished or contribute to it :)