Re: st: Loop for creating a sum of previous observations in an unbalanced panal data set

[Eric Booth <ebooth@ppri.tamu.edu>]

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Kaspar, here's one solution:

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clear
//1.  create some fake date data to work with//
set obs 1000
g date = date("01/01/2008", "MDY") in 1
	replace date = date[_n-1]+1 in 2/l
	format date %td
forval n = 1/3 {
g value`n' =  int(((`n'*50)+1)*runiform())
		}	

//2. create running sum for prev 90 days for value1 only//
sort date
g sum3m_value1 = .

forval n = 1/`=_N' {
	cap drop i`n'
	g i`n' = 1 if  date[`n']>=date & (date[`n']-date) <= 90
	egen sum3m_value1`n' = total(value1) if i`n'==1
	replace sum3m_value1 = sum3m_value1`n' if mi(sum3m_value1)
	drop  i`n'
	drop sum3m_value1`n'
	}
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