how to find "first" or "last" record after sort in R
Thanks Therneau,?duplicated() function works well. --- Kai
On Friday, September 10, 2021, 05:13:47 AM PDT, Therneau, Terry M., Ph.D. <therneau at mayo.edu> wrote:
I prefer the duplicated() function, since the final code will be clear to a future reader. ? (Particularly when I am that future reader). last <- !duplicated(mydata$ID, fromLast=TRUE)? # point to the last ID for each subject mydata$data3[last] <- NA Terry T. (I read the list once a day in digest form, so am always a late reply.)
On 9/10/21 5:00 AM, r-help-request at r-project.org wrote:
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 ??? [[alternative HTML version deleted]]