Combine two time and date variables, and creating a yearly (readable) variable

[Cathrine Christiansen]

Dear stata community

I have a data-set that is combined from two different datasets, by append. I have a variable for time and date in each of the original datasets, and now I have two variables with time and date. How can I combine these (they have the same format)? And then I want to make a new variable that shows only the year, so I can sort observations within a patientID, on year.

* Example generated by -dataex-. For more info, type help dataex
clear
input str9 PatientID float(dato2 date2)
"1" 19981     .
"1" 20394     .
"2" 20922     .
"2"     . 20149
"2"     . 19308
"3"     . 20579
"3" 19756     .
"4" 20579     .
"4"     . 19471
"4" 19797     .
end
format %tdCCYY-NN-DD dato2
format %tdCCYY-NN-DD date2

Cathrine

[Fei Wang]

gen date = cond(mi(dato2), date2, dato2)
format date %tdCCYY-NN-DD
gen year = yofd(date)

It would be better to unify variable names before appending them.

[Nick Cox]

  
 gen date = min(date2, dato2)

would also work fine with this example.

A paranoid check for two non-missing values could be

list data?2  if !missing(dato2, date2)

[Cathrine Christiansen]

Thank you so much! I also unified the variables before appending them, so that was helpful.