st: RE: How to drop observations

[Nick Cox <n.j.cox@durham.ac.uk>]

This is two questions not one. 

1. Keeping only firms who switch. 

bysort firm (year) : drop if status[1] == status[_N] 

Those firms have the same status at the end as the beginning. 

bysort firm (status) : drop if status[1] == status[_N] 

Those firms never change their status. 

Or 

bysort firm : keep if status[1] == 0 & status[_N] == 1 

for 0 to 1 switches from beginning to end. 

See also the FAQ

http://www.stata.com/support/faqs/data/diff.html

which is just a twist away from your problem. Did you search the FAQs before posting? 

2. Keeping only part of a panel. I am not clear about your exact rules, but check out the data management FAQs. 

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

natasha agarwal

I want to estimate a model only on those firms where the exporting
status switches from non-export to export.So for instance.

Firm Year Export Status
A      2001    0
A      2002    0
A      2003    0
A      2004    1
A      2005    1
B      2001    0
B      2002    0
B      2003    0

In this I want to drop firm B as it does not change its export status.
Moreover, for firm A, I want to keep only observation uptil 2004.


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