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From |
Clyde B Schechter <clyde.schechter@einstein.yu.edu> |

To |
"statalist@hsphsun2.harvard.edu" <statalist@hsphsun2.harvard.edu> |

Subject |
Re: st: generating a variable that requires comparing two dates |

Date |
Fri, 12 Apr 2013 15:11:45 +0000 |

Ariel Linden wrote: ... I would like to generate a new variable ( by ID) that will equal 1 if there was an alert (triggered on the surveydate, when that surveydate was the same as the admitdate. The obvious problem is that the dates are not always aligned so a straight "bys ID: gen test if surveydate==admitdate & alert==1" will not always work. In the data below, the code would need to "see" that the admitdate of 4/6/2011 has a corresponding surveydate a few lines down where the alert==1. Similarly, the next admitdate is 4/20/2011, so it would need to lookup the corresponding surveydate and verify that alert==1. ... **** example data**** ID surveydate alert admitdate 1 4/2/2011 1 4/6/2011 1 4/3/2011 1 4/20/2011 1 4/4/2011 0 4/20/2011 1 4/5/2011 0 4/20/2011 1 4/6/2011 1 4/20/2011 1 4/7/2011 0 4/20/2011 1 4/8/2011 0 4/20/2011 1 4/9/2011 0 4/20/2011 1 4/10/2011 0 4/20/2011 1 4/11/2011 0 4/20/2011 1 4/12/2011 0 4/20/2011 1 4/13/2011 0 4/20/2011 1 4/14/2011 0 4/20/2011 1 4/15/2011 0 4/20/2011 1 4/16/2011 0 4/20/2011 1 4/17/2011 0 4/20/2011 1 4/18/2011 0 4/20/2011 1 4/19/2011 0 4/20/2011 1 4/20/2011 1 4/20/2011 1 4/21/2011 0 4/20/2011 How about: tempfile surveyalertdates preserve keep if alert == 1 keep id surveydate /* DEPENDING ON YOUR DATA YOU NEXT SHOULD DO EITHER isid id surveydate OR duplicates drop */ rename surveydate alertdate save `surveyalertdates' restore gen alertdate = admitdate merge 1:1 id alertdate using `surveyalertdates', keep(match master) gen test = (_merge == 3) The later question about identifying the situation where the alert occurred 1 day before admitdate just requires modifying the gen alertdate... statement in the above. Hope this helps. Clyde Schechter Dept. of Family & Social Medicine Albert Einstein College of Medicine Bronx, NY, USA * * 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/

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