st: nested calculations

[Fabio Zona <fabio.zona@unibocconi.it>]

Hi All,
I have another little problem: promise it is the last one for today! 

I have the list below. For each firm, I have to calculate the standard deviation for every variable (e.g., for Var 1) referring to the 4 quarters of each year!
Below you find both the starting matrix and the expected one.

Please, help! (I think this might be easier)


STARTING MATRIX OF VAR/OBS
firm   year  quarter  	Var1	Var2
1	1	1		
1	1	2		
1	1	3		
1	1	4		
1	2	1		
1	2	2		
1	2	3		
1	2	4		
1	3	1		
1	3	2		
1	3	3		
1	3	4		
2	1	1		
2	1	2		
2	1	3		
2	1	4
2	2	1
2	2	2
2	2	3
2	2	4
2	3	1
2	3	2
2	3	3
2	3	4



EXPECTED MATRIX OF VAR/OBS
firm   year  stddev_Var1
1       1        number
1       2
1       3
2       1
2       2
2       3



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