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st: RE: Re: Average and count from a given number of previous observations


From   "Nick Cox" <n.j.cox@durham.ac.uk>
To   <statalist@hsphsun2.harvard.edu>
Subject   st: RE: Re: Average and count from a given number of previous observations
Date   Tue, 11 Dec 2007 19:14:38 -0000

This can be done more directly without any loops or 
multiple new variables. 

Generate the cumulative rainfall 

. gen curain = sum(rain) 

The rain in the previous 28 days is then 

. gen prev28 = curain[_n-1] - curain[_n-29] 

subject to details about the precise definition. 

I learned this trick from Michael Blasnik. 

Nick
n.j.cox@durham.ac.uk 

Steven Proud

One way of doing this would be with a loop

so, could:
tsset date
local i=1
while `i'<=84 {
gen l`i'rainfall=l`i'.rainfall
local i=`i'+1
}
gen lag28rainfall=rsum(l1rainfall-l28rainfall)
gen lag84rainfall=rsum(l1rainfall-l84rainfall)
drop l1rainfall-l84rainfall


gen rain=0
replace rain=1 if rainfall>0
local i=1
while `i'<=84 {
gen l`i'rain=l`i'.rain
local i=`i'+1
}

gen lag28rain=rsum(l1rain-l28rain)
gen lag84rain=rsum(l1rain-l84rain)
drop l1rain-l84rain

I think that should work


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