st: creating new variable

["S.H. Former" <S.H.Former@uvt.nl>]

Dear reader,
I have a question regarding the composition of my database. I want to know whether it is possible to incorporate the following variable. I want to create a variable that counts previous observations but only till five years back. Let me explain it using a part my database which looks as follows:

gvkey	appyear	
1004	1985
1004	2001
1010	1977
1010	1977
1010	1977
1010	1977
1010	1977
1010	1977
1010	1977
1010	1978
1010	1978
1010	1978
1010	1978
1010	1978
1010	1978
1010	1978
1010	1978
1010	1978
1010	1978
1010	1978
1010	1979
1010	1979
1010	1979
1010	1979
1010	1979
1010	1979
1010	1979
1010	1979
1010	1979

Now I want a new variable that counts the number of observations for each Gvkey (so it has to be counted for each Gvkey) where the number of observations is counted until five years back. So the new variable should look like this:

 gvkey	appyear			New Variable		Comment
1004	1985			0			 no observations before
1004	2001			0			longer than five years ago		
1010	1977			0			no observations
1010	1977			0			no observations
1010	1977			0			no observations
1010	1977			0			no observations		
1010	1977			0			no observations
1010	1977			0			no observations
1010	1977			0			no observations
1010	1978			7			number of observations in 1977 by Gvkey 1010
1010	1978			7			number of observations in 1977 by Gvkey 1010
1010	1978			7			number of observations in 1977 by Gvkey 1010
1010	1978			7			number of observations in 1977 by Gvkey 1010
1010	1978			7			number of observations in 1977 by Gvkey 1010
1010	1978			7			number of observations in 1977 by Gvkey 1010
1010	1978			7			number of observations in 1977 by Gvkey 1010
1010	1978			7			number of observations in 1977 by Gvkey 1010
1010	1978			7			number of observations in 1977 by Gvkey 1010
1010	1978			7			number of observations in 1977 by Gvkey 1010
1010	1978			7			number of observations in 1977 by Gvkey 1010
1010	1979			18		number of observation in 1977 and 1978 by Gvkey 1010
1010	1979			18		number of observation in 1977 and 1978 by Gvkey 1010
1010	1979			18		number of observation in 1977 and 1978 by Gvkey 1010
1010	1979			18		number of observation in 1977 and 1978 by Gvkey 1010
1010	1979			18		number of observation in 1977 and 1978 by Gvkey 1010
1010	1979			18		number of observation in 1977 and 1978 by Gvkey 1010
1010	1979			18		number of observation in 1977 and 1978 by Gvkey 1010
1010	1979			18		number of observation in 1977 and 1978 by Gvkey 1010
1010	1979			18		number of observation in 1977 and 1978 by Gvkey 1010
Of course, the comment would not have to be included but is to make the problem clear to you! Hope you can help me,

Kind regards,
Sytze



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