Dropping observations if missing certain dates

[Jack Reimer]

I have incomplete data and would like to drop any observations for which I do not have data in a particular variable during a given time period. My best guess of how to do this would be by generating a tag with bysort and then dropping everything without that tag. For example,

clear all
ssc install dataex
input long id float year float month float day float var1
1 2017 7 1 125
1 2017 8 1 200
1 2017 9 1 108
1 2018 4 1 20
1 2018 5 1 50
1 2018 7 1 73
1 2018 8 1 18
1 2018 9 1 20
2 2018 7 1 32
2 2018 8 1 29
2 2018 9 1 18
2 2018 4 1 103
2 2018 5 1 24
2 2018 7 1 .
2 2018 8 1 .
2 2018 9 1 .
3 2017 7 1 20
3 2017 8 1 .
3 2017 9 1 .
3 2018 7 1 73
3 2018 8 1 18
3 2018 9 1 20
end

Where if I only want to keep observations that have no missing data in var1 for the months of July, August and September (7,8,9) in 2018, the final output ought to be

clear all
ssc install dataex
input long id float year float month float day float var1
1 2017 7 1 125
1 2017 8 1 200
1 2017 9 1 108
1 2018 4 1 20
1 2018 5 1 50
1 2018 7 1 73
1 2018 8 1 18
1 2018 9 1 20
3 2017 7 1 20
3 2017 8 1 .
3 2017 9 1 .
3 2018 7 1 73
3 2018 8 1 18
3 2018 9 1 20

Thank you very much for your help.

[Wouter Wakker]

I don't think bysort is necessary, I think you're looking for something like this:

gen tag = missing(var1) & inrange(month,7,9) & year == 2018
drop if tag

or just -drop if- with the right conditions, but generating a tag first allows you to check whether it will really drop the observations you want.