Hello List,
Please look at the sample data frame below:
ID date1 date2 date3
1 2015-10-08 2015-12-17 2015-07-23
2 2016-01-16 NA 2015-10-08
3 2016-08-01 NA 2017-01-10
3 2017-01-10 NA 2016-01-16
4 2016-01-19 2016-02-24 2016-08-01
5 2016-03-01 2016-03-10 2016-01-19
This data frame was sorted by ID and date1. I need to set the column date3 as
missing for the "last" record for each ID. In the sample data set, the ID 1, 2,
4 and 5 has one row only, so they can be consider as first and last records.
the data3 can be set as missing. But the ID 3 has 2 rows. Since I sorted the
data by ID and date1, the ID=3 and date1=2017-01-10 should be the last record
only. I need to set date3=NA for this row only.
the question is, how can I identify the "last" record and set it as NA in date3
column.
Thank you,
Kai
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