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2011 Aug 24
3
Creating new variable with maximum visit date by group_id
Dear R users,
I am encoutering the following problem: I have a dataset with a 'unique_id' and different 'visit_date' (formatted as.Date, "%d/%m/%Y") per unique_id. I would like to create a new variable with the most recent date of visit per unique_id as shown below.
unique_id visit_date last_visit_date
1 01/06/2010 01/06/2011
1 01/01/2011 01/06/2011
1 01/06/2011 01/06/2011
2 01/01/2...