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st: Re: question about working with dates and times


From   "Joseph Coveney" <jcoveney@bigplanet.com>
To   <statalist@hsphsun2.harvard.edu>
Subject   st: Re: question about working with dates and times
Date   Tue, 27 Jul 2010 10:58:25 +0900

Paul Visintainer wrote:

I'm having a little difficulty working with dates and times as doubles.  I want
to add to an existing date an interval that is 24 hours (or even larger).  The
following code works:

.gen double day0 = tc("06oct2007 00:00:00")     // e.g., existing date   (1)

.gen double day1 = day0 + tc(23:59:59) + tc(00:00:01)  // 24-hr interval (2)

.format day0 day1 %tc

.list day0 day1 in 1

     +-----------------------------------------+
     |               day0                 day1 |
     |-----------------------------------------|
  1. | 06oct2007 00:00:00   07oct2007 00:00:00 |
     +-----------------------------------------+

But, step 2 seems cumbersome (because tc(24:00:00) is an invalid value.)

When working with dates/times as doubles, I suspect there is a simpler approach
for adding large intervals (e.g., 36 hours, or 2 weeks, or 3 months, etc).  Any
help would be appreciated.

--------------------------------------------------------------------------------

Use Stata's base date-time, midnight, January 1, 1960, as the zero-point in the 
increment.

Joseph Coveney

. generate double day0 = tc("06oct2007 00:00:00")

. generate double day1 = day0 + ///
>     tc("02jan1960 00:00:00")

. generate double day2 = day0 + ///
>     tc("02mar1960 00:00:00")

. format day0 day1 day2 %tc

. list day0 day1 day2 in 1

     +--------------------------------------------------------------+
     |               day0                 day1                 day2 |
     |--------------------------------------------------------------|
  1. | 06oct2007 00:00:00   07oct2007 00:00:00   06dec2007 00:00:00 |
     +--------------------------------------------------------------+



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