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RE: st: Subtracting in Variable by a Group


From   Arya Eskamani <Arya.Eskamani@assist-rx.com>
To   "statalist@hsphsun2.harvard.edu" <statalist@hsphsun2.harvard.edu>
Subject   RE: st: Subtracting in Variable by a Group
Date   Fri, 29 Mar 2013 21:53:23 +0000

Wow...it seems so evident now that I'm actually disappointed in  myself :) thank you very much! It worked like a charm.

Arya Eskamani, M.S.
Project Manager
4700 Millenia Blvd | Ste 500 | Orlando, FL 32839
407.367.2880 Phone | 877.313.4412 eFax 
www.assist-rx.com | arya.eskamani@assist-rx.com


-----Original Message-----
From: owner-statalist@hsphsun2.harvard.edu [mailto:owner-statalist@hsphsun2.harvard.edu] On Behalf Of Nick Cox
Sent: Friday, March 29, 2013 12:16 PM
To: statalist@hsphsun2.harvard.edu
Subject: Re: st: Subtracting in Variable by a Group

Your do-file could consist of

bysort group (date): gen time = date - date[_n-1]

but many Stata users would just type that one command.


Nick

On 29 Mar 2013, at 16:10, Arya Eskamani <Arya.Eskamani@assist-rx.com>
wrote:

> Hello and thank you in advance
>
> I'm attempting to find the difference in days between events within 
> different groups.  The date is formatted %td (daily). Here's an 
> example of my dataset:
>
> group    event    date
> A    1    08mar2013
> A    2    10mar2013
> A    3    15mar2013
> B    1    10sep2012
> B    2    15sep2012
> C    1    07aug2011
> C    2    23aug2011
> C    3    23aug2011
> C    4    24aug2011
> D    1    25dec2012
> E    1    01jan2013
>
> I want to generate a new variable, say "time" , that calculates the 
> difference in days from one event occurring to the next event in 
> between the groups.  For example, in group A there are 2 days between 
> even 1 and event 2 and then 5 days from event 2 to event 3, and 
> similarly for others.  The example below shows what I'm trying to 
> achieve:
>
> group    event    date    time
> A    1    08mar2013    .
> A    2    10mar2013    2
> A    3    15mar2013    5
> B    1    10sep2012    .
> B    2    15sep2012    5
> C    1    07aug2011    .
> C    2    23aug2011    16
> C    3    23aug2011    0
> C    4    24aug2011    1
> D    1    25dec2012    .
> E    1    01jan2013    .
>
> Notice that the time variable is blank for 1st events because there is 
> no previous event to subtract from.  I've never ran an operation 
> within a column before and have been doing this in excel but would 
> like to just write a do file on this.  Any help is much appreciated.  
> Thank you again.
>
>
> Arya Eskamani
>
>
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