[R] how to find "first" or "last" record after sort in R
r@oknz @end|ng |rom gm@||@com
Sat Sep 11 03:20:28 CEST 2021
Let's simplify this to consider a single vector, such as
x <- c(1,1,1,2,2,3,3,3,3,4,5,5,5)
in which equal elements are in contiguous blocks.
 0 0 1 0 1 0 0 0 1 1 0 0
Of course, there could be gaps, or the sequence might be descending
instead of ascending. So
> diff(x) != 0
We are nearly there, but there is a problem.
The last element of the vector is always the last element of a group,
but it will never be reported, because there is no following element
to compare it with. So
> c(diff(x) != 0, TRUE)
That gives us a logical vector which we can use in indexing.
> w <- c(diff(x) != 0, TRUE)
> x[w] <- NA
 1 1 NA 2 NA 3 3 3 NA NA 5 5 NA
On Fri, 10 Sept 2021 at 07:00, Kai Yang via R-help <r-help 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,
> [[alternative HTML version deleted]]
> R-help using r-project.org mailing list -- To UNSUBSCRIBE and more, see
> PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.
More information about the R-help