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Re: st: Subtracting in Variable by a Group
From
Nick Cox <[email protected]>
To
"[email protected]" <[email protected]>
Subject
Re: st: Subtracting in Variable by a Group
Date
Fri, 29 Mar 2013 16:16:16 +0000
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 <[email protected]>
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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