st: forvalues + egen rsum with missing variables

[Florian Seliger <florian.seliger@gmx.de>]

Dear Statalist,

I'm trying to use the following command on a couple of datasets:

egen id_max=max(id)
local l=id_max

forvalues j=1960(1)2009 { 	//years
forvalues k=1(1)`l' {			//number of IDs
egen a_`j'=rsum(a_`j'_`k' - a_`j'_`l')
	}
	}

********


The problem is that a dataset doesn't contain all years from 1960 to 2009, but only a subset, e.g. 1961, 1985, 1994 etc. In addition, the number of IDs varies (therefore, I need `l' as a maximum) and each year can only be assigned a subset of IDs (they are not assigned in a consistent way).
To give an example, I might have the following variables in the dataset:
a_1990_63                                 
a_1990_64                     
a_1990_65                         
a_1990_66                      
a_1990_67                      
a_1990_68                   
a_1990_69

 a_1994_1                          
a_1994_2                   
a_1994_3                        
a_1994_4                       
a_1994_5                       
a_1994_6                          
a_1994_7                         
a_1994_8                        
a_1994_9        ... etc.

How can I proceed in order to calculate the row sum for each year? I have tried to use "capture", but it didn't work. 

Thanks a lot,
Florian
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