I have a large dataset containing many dates per participant. I want to creat a new variable containing the number of unique dates per participant. I have been trying to figure this out but it does not work. An example of how the dataset looks like you see below:
participant 1 - date.1 - date.2 - date.3 - date.4 ... date.412
participant 2 - date.1 - date.2 - date.3 - date.4 ... date.412
Dates are in the format: 31-oct-20
Some participants have only 10 dates, others have 412 dates
Any idea how I can create this new variable containing the number of unique dates?
In R, you can use "unique" command to extract the unique dates from your data:
uniqueDates
I have a YouTube video on how to enter variables manually. This might be useful.
https://www.youtube.com/watch?v=Yp5w2fDDYpM&t=843s&ab_channel=Dr.S.RamaGokulaKrishnan
In general, you can sort the date variable, then create a variable that is 1 if the date is not the same as the preceding observation and zero otherwise.
. sort date
. gen unique=date==date[_n-1]
would be the Stata code. Note that the very first observation has no preceding observation and will have to be tidied by hand. In Stata you could write
. gen unique=date==date[_n-1] | (_n==1)
which is a kludge but it works.
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