Message-ID: <6315bd$gjsu9b@ironport10.mayo.edu>
Date: 2021-09-10T12:13:45Z
From: Terry Therneau
Subject: how to find "first" or "last" record after sort in R
In-Reply-To: <mailman.364180.1.1631268001.4139.r-help@r-project.org>
I prefer the duplicated() function, since the final code will be clear to a future reader.
(Particularly when I am that future reader).
last <- !duplicated(mydata$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
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