[R] how to find "first" or "last" record after sort in R
y@ngk@|9999 @end|ng |rom y@hoo@com
Fri Sep 10 17:51:39 CEST 2021
Thanks Therneau, duplicated() function works well. --- Kai
On Friday, September 10, 2021, 05:13:47 AM PDT, Therneau, Terry M., Ph.D. <therneau using 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
(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 using 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,
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