st: counting observations

[Jurgen Sidgman <sidgman@uwm.edu>]

Hi,

I have a dataset that has observations for each day of many months. What I need to do is: for each month I need to add all observations for each of the previous 3 months. For example, for january I need to add all observations from October to December from the previous year. Next, for february I need to add all observations from November to January and so on. What I have been doing so far is calculating the cumulative value for each month as follows:

. sort obsdate
. egen count_obs = count(obsdate) if year(obsdate) == 2004 & month(obsdate) <= 3 (this is for the first time I perform the calculation)