topic Re: Code/algorithm to determine if a date/time was during Daylight Savings Time in SAS Programming

Code/algorithm to determine if a date/time was during Daylight Savings Time

PaigeMiller — Wed, 22 May 2013 19:44:17 GMT

Anybody know of SAS code, or mathematical algorithm, that can determine if a date/time value was during Daylight Savings Time or not?

Thanks.

Re: Code/algorithm to determine if a date/time was during Daylight Savings Time

PGStats — Wed, 22 May 2013 19:59:51 GMT

Anywhere on Earth?

Re: Code/algorithm to determine if a date/time was during Daylight Savings Time

PaigeMiller — Wed, 22 May 2013 20:05:46 GMT

Well, yes, that would be nice; although I would settle for code or algorithm that works in Rochester, NY

I should add that the code or algorithm that I hope to find would work going back for at least a decade.

Re: Code/algorithm to determine if a date/time was during Daylight Savings Time

PGStats — Thu, 23 May 2013 22:33:23 GMT

Here is how I would code it for years >= 2007 (the change dates were different before). If you want datetimes, you will have to take into account that the switch occurs at 2AM.

data want(drop=year);
format myDate DSTbegin DSTend date9.;
call streaminit(23356);
do year = 2007 to 2025;
     /* random date */
     myDate = intnx("DAY", mdy(1,1,year), floor(rand("UNIFORM")*364));
     /* second Sunday of March */
     DSTbegin = intnx("WEEK", intnx("DAY",mdy(3, 1, year(myDate)), -1), 2);
     /* first Sunday of November */
     DSTend = intnx("DAY",intnx("WEEK", mdy(10, 31, year(myDate)), 1), -1);
     DST = DSTbegin <= myDate <= DSTend;
     output;
     end;
run;

proc print; id myDate; run;

You can check the dates against

http://en.wikipedia.org/wiki/Daylight_saving_time_in_the_United_States

Re: Code/algorithm to determine if a date/time was during Daylight Savings Time

PaigeMiller — Fri, 24 May 2013 12:12:12 GMT

Thanks!

Impressive work! I will have to see if I can adapt this to pre-2007.

By the way, there appears to be errors in DSTend, they are off by a day on a couple of years. I'll have to see if I can come up with a fix

Re: Code/algorithm to determine if a date/time was during Daylight Savings Time

PGStats — Fri, 24 May 2013 12:18:27 GMT

DSTend is not the first day of the non-DST period, it is the last DST day, the day before. I choose to use that date so that it could be used in a SQL condition like WHERE date BETWEEN DSTbegin AND DSTend. - PG

Re: Code/algorithm to determine if a date/time was during Daylight Savings Time

Rick_SAS — Fri, 24 May 2013 12:20:46 GMT

See Computing the onset and end of daylight saving time in SAS: The EASY way! - The DO Loop

An earlier version ( Spring forward, fall back: Using SAS to compute the onset of daylight saving time - The DO Loop) used PG's approach.

Re: Code/algorithm to determine if a date/time was during Daylight Savings Time

PaigeMiller — Fri, 24 May 2013 15:39:57 GMT

Great stuff, Rick! Thanks

Re: Code/algorithm to determine if a date/time was during Daylight Savings Time

jwsquillace — Fri, 24 May 2013 15:44:38 GMT

Here is a published sample that accounts for before and after 2007:

Sample 24735: Compute daylight saving time

http://support.sas.com/kb/24735

Cheers, Jan