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