On Fri, Jul 23, 2010 at 12:35 PM, <murali.me...@avivainvestors.com> wrote:
> David, Stephen,
> You're right - it's the time zone conventions that threw me as well. I tried
> those round() operations earlier, but inevitably ended up being either an
> hour behind. Even when I specified my time zone, it didn't make any
> difference. So there's something else that I'm missing. I'll take a look at
> your various approaches, and get back to you.
Does your problem really involve time zones? If not you would likely
be best off using a datetime class that has no time zone so you don't
run into this problem in the first place. Also its particularly easy
with chron due to the availability of trunc.times() :
library(chron)
now <- as.chron(format(Sys.time()))
trunc(now + as.numeric(times("00:15:00")), "00:30:00")
With POSIXct you could muck with the internals like this (which uses
the fact that there are 1800 seconds in an half hour):
x <- Sys.time()
structure(1800 * (as.numeric(x + 900) %/% 1800), class = class(x))
See the article in R News 4/1 for more.
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