Notice: On April 23, 2014, Statalist moved from an email list to a forum, based at statalist.org.
| From | Arya Eskamani <Arya.Eskamani@assist-rx.com> |
| To | "statalist@hsphsun2.harvard.edu" <statalist@hsphsun2.harvard.edu> |
| Subject | st: Subtracting in Variable by a Group |
| Date | Fri, 29 Mar 2013 16:10:01 +0000 |
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 * * For searches and help try: * http://www.stata.com/help.cgi?search * http://www.stata.com/support/faqs/resources/statalist-faq/ * http://www.ats.ucla.edu/stat/stata/