# st: Re: How to detect the change of i over t?

 From "Martin Weiss" <[email protected]> To <[email protected]> Subject st: Re: How to detect the change of i over t? Date Sun, 8 Feb 2009 10:52:24 +0100

```<>

See NJC`s FAQ: http://www.stata.com/support/faqs/data/panel.html

*********
clear*
set obs 20
egen float id = seq(), from(1) to(4) block(5)
egen float t = seq(), from(1) to(5) block(1)
g x=cond(runiform()<=0.5,0,1)
g byte become=.
bys id: replace become=cond(x[_n-1]==0 & x[_n]==1,1,0)
list, noo sepby(id)
***********

HTH
Martin
_______________________
```
----- Original Message ----- From: "Benson Limann" <[email protected]>
```To: "stata" <[email protected]>
Sent: Sunday, February 08, 2009 5:46 AM
Subject: st: How to detect the change of i over t?

```
```Hi all:

```
I am using an unbalanced panel dataset. i is ID and t is time. Every (i,t) has a characteristic x=0 or 1.
```
I want to generate a variable called "become" such that for each (i,t):

become=1, if x=0 at time t-1, and x=1 at time t
become=0, otherwise

```
How to write it? My primary concern is how to deal with the first t for each i--this observation does not have t-1.
```
Any suggestion would be greatly appreciated.

Ben

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```
```
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