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RE: st: How do I drop first and last observations please?


From   Lucie Vlach <Lucie.Vlach@albertahealthservices.ca>
To   "statalist@hsphsun2.harvard.edu" <statalist@hsphsun2.harvard.edu>
Subject   RE: st: How do I drop first and last observations please?
Date   Mon, 18 Jul 2011 14:40:55 -0600

Thank you Nick!
drop in 1 and drop in L worked great, and for now, the datasets are small. They may get bigger in the future.

Lucie

________________________________________
From: owner-statalist@hsphsun2.harvard.edu [owner-statalist@hsphsun2.harvard.edu] On Behalf Of Nick Cox [njcoxstata@gmail.com]
Sent: July 18, 2011 2:03 PM
To: statalist@hsphsun2.harvard.edu
Subject: Re: st: How do I drop fist and last observations please?

drop in 1
drop in L

If the datasets are all small, then

drop if _n == 1 | _n == _N

should be about as fast. For a big dataset, that is probably a bad
idea, as Stata will test to see if every observation satisfies the
-if-.

Nick

On Mon, Jul 18, 2011 at 1:37 PM, Lucie Vlach
<Lucie.Vlach@albertahealthservices.ca> wrote:

> I need to drop my first and last observation from a data set in a do file.
> Not all datasets will have the same number of observations. Is there a good ‘drop’ command that will do this for me, regardless how long my dataset is? It will always be the first and last observation.
>
> Here is the example of my data:
>
> Record_Type Sub_Prefix Current_Yr Source Sequence_Number Check_Digit Transaction_Type Segment_Type Segment_Sequence Action_Code Unused Claim_Type Service_Provider_ULI Skill_Code Service_Recipient_ULI
> 2 UCM 00 00 80
> 3 UCM 11 00 00546733 4 CIP1 CIB1 0001C   RGLR 3535446208 PSYC 352543330
> 3 UCM 11 00 0037920 6 CIP1 CIB1 0001A   RGLR 2296454208 GP 445454551
> 4 UCM 00 00 8000143 0 0000 144
>
> Here I want to drop: “2 UCM 00 00 80” and “4 UCM 00 00 8000143 0 0000 144”
>

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