Hello,

I am new to Stata. Can you please help me with the following issue: for different companies, which I labeled as id, I have different variables describing some stock characteristics.
I would like to keep the companies that have data for the stock characteristics for every month within a year.
The issue is that the data does not appear as missing, is just simply absent.
For example, if we consider the year 2017, I have the following entries for the dates: date id
31jan2017 1
28feb2017 1
31mar2017 1
30apr2017 1
31may2017 1
30jun2017 1
31jul2017 1
31aug2017 1
30sep2017 1
31oct2017 1
30nov2017 1
31dec2017 1

and then data entries for other variables.
How do I drop observations that have only 3 entries for the dates above, as opposed to 12, e.g. for id=2, I only have observations for 28feb2017, 30apr2017 and 30sep2017?

I thought about doing a bysort by id and date, i.e. bysort id (date): drop if
but I don't know how to write the condition, as the data is not missing ., but simply not present.

Thank you for your help.