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# Re: st: recursive variable for many groups

 From n j cox To statalist@hsphsun2.harvard.edu Subject Re: st: recursive variable for many groups Date Thu, 22 Sep 2005 15:10:43 +0100

```Two answers:

1. Use -tsset- and exploit Stata's time-series operators.

tsset group time
gen x = y
replace x = constant * L.x

2. Use -if- not -in-.

gen x = y
bysort group (time): replace x = constant * x[_n-1] if _n > 2

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

Bjorn Persson <bpersson@bu.edu>

I am trying to create a variable that depends on its lagged values, and
I received this very helpful tip from Statalist:

gen x = y in 1

replace x = constant*x[_n-1] in 2/l(ast)

I am now wondering how to to this for different groups. That is,

gen x(i) = y(i) in 1(i)

replace x(i) = constant*x(i)[_n-1] in 2(i)/l(i)

for groups i=1,2,3...

I have tried to sort the data using "by", but the "by" command does not
allow the "in" specification.

*
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```

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