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Asked: 2026-05-28T05:27:54+00:00

In PHP (since 5.2.0) I can write this code: //$t is timestamp of day

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In PHP (since 5.2.0) I can write this code:

//$t is timestamp of day I want to look at
$tz=new DateTimeZone('America/New_York');
$transition = $tz->getTransitions($t,$t);
if(!$transition || count($transition)==0)throw new Exception("Bad timezone")
$offset=$transition[0]['offset'];   //This is seconds ahead of GMT.
      //I.e. -14400 in summer, -18000 in winter.

I nearly cried with joy when I discovered this class/idiom; but is there a way to do the same thing in R? Or do I have to resort to what I used to do in PHP, which was hard-code an array of summertime start/end dates for each timezone I need to consider?

(BTW, for more on the PHP code, see: How to tell if a timezone observes daylight saving at any time of the year? )

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1 Answer

  1. Editorial Team

    With as.POSIXct and as.POSIXlt you can get this information. For example:

    tz = 'Europe/Madrid'
d1 <- as.POSIXct('2010-01-01 12:00:00',  tz = tz)
as.POSIXlt(d1)$isdst ## 0 since it's not DST

    If you need the difference from UTC:

    d0 <- as.POSIXct(format(d1,  tz = 'UTC'),  tz = tz)
as.numeric(d1 - d0) ## 1 hour

    The same for another day:

    d2 <- as.POSIXct('2010-07-01 12:00:00',  tz = tz)
as.POSIXlt(d2)$isdst ## 1 since it is DST
d0 <- as.POSIXct(format1(d2,  tz = 'UTC'),  tz = tz)
as.numeric(d2 - d0) ## 2 hour
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