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st: RE: using the first n observations in a dataset w/o evaluating the whole thing?


From   "Kieran McCaul" <kamccaul@meddent.uwa.edu.au>
To   <statalist@hsphsun2.harvard.edu>
Subject   st: RE: using the first n observations in a dataset w/o evaluating the whole thing?
Date   Fri, 4 Apr 2008 07:54:44 +0800

Try:
use in 1/100 using mydata, clear

______________________________________________
Kieran McCaul MPH PhD
WA Centre for Health & Ageing (M573)
University of Western Australia
Level 6, Ainslie House
48 Murray St
Perth 6000
Phone: (08) 9224-2140
Phone: -61-8-9224-2140
email: kamccaul@meddent.uwa.edu.au
http://myprofile.cos.com/mccaul 
_______________________________________________


-----Original Message-----
From: owner-statalist@hsphsun2.harvard.edu
[mailto:owner-statalist@hsphsun2.harvard.edu] On Behalf Of Rodini, Mark
Sent: Friday, 4 April 2008 7:32 AM
To: statalist@hsphsun2.harvard.edu
Subject: st: using the first n observations in a dataset w/o evaluating
the whole thing?

Greetings.

Suppose I have a large Stata dataset (e.g. 3,000,000 observations) and I
only with to read in the first, say, 100 observations.

I have tried the code, which works:

use mydata if ( _N<100 )

However, evidently, this code goes through ALL 3 million observations to
evaluate the expression in parentheses, which can be very time consuming
(and sort of defeats the purpose).  Is there a way to only read the
first 100 observations without having to evaluate the entire dataset?

Perhaps some application of the "set obs 100"?  But I have not been
successful. 

Thank you.
-Mark

----------------------------------------------
Mark Rodini
mrodini@compasslexecon.com
 

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