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. Cheers, Murali
-----Original Message----- From: r-help-boun...@r-project.org [mailto:r-help-boun...@r-project.org] On Behalf Of David Winsemius Sent: 23 July 2010 17:15 To: stephen sefick Cc: r-help@r-project.org Subject: Re: [R] converting a time to nearest half-hour On Jul 23, 2010, at 12:04 PM, stephen sefick wrote: > If you have a zoo series this should work. If it doesn't then please > tell me because I think it works. > > snap2min <- function(zoo, min="00:15:00"){ > min15 <- times(min) > a <- aggregate(zoo, trunc(time(zoo), min15), function(x) mean(x, > na.rm=TRUE)) > } This "works" for producing 10 half-hour intervals of EDT times: as.POSIXct(60*30*( round( as.numeric( Sys.time()+ 60*30*(1:10))/ # the sequence creation (60*30))) - # divide prior to rounding 5*60*60, # the TZ offset origin="1970-01-01" ) [1] "2010-07-23 12:30:00 EDT" "2010-07-23 13:00:00 EDT" [3] "2010-07-23 13:30:00 EDT" "2010-07-23 14:00:00 EDT" [5] "2010-07-23 14:30:00 EDT" "2010-07-23 15:00:00 EDT" [7] "2010-07-23 15:30:00 EDT" "2010-07-23 16:00:00 EDT" [9] "2010-07-23 16:30:00 EDT" "2010-07-23 17:00:00 EDT" > > hth > > Stephen Sefick > > On Fri, Jul 23, 2010 at 11:00 AM, David Winsemius > <dwinsem...@comcast.net> wrote: >> >> On Jul 23, 2010, at 11:35 AM, David Winsemius wrote: >> >>> >>> On Jul 23, 2010, at 11:20 AM, <murali.me...@avivainvestors.com> >>> <murali.me...@avivainvestors.com> wrote: >>> >>>> Hi folks, >>>> >>>> I've got a POSIXct datum as follows: >>>> >>>>> Sys.time() >>>> >>>> [1] "2010-07-23 11:29:59 BST" >>>> >>>> I want to convert this to the nearest half-hour, i.e., to >>>> "2010-07-23 >>>> 11:30:00 BST" >>>> >>>> (If the time were "11:59:ss", I want to convert to "12:00:00"). >>>> >>>> How to achieve this? >>> >>> Couldn't you just coerce to numeric, divide by 60(sec)*30(half-hour >>> minutes), round to integer, multiply by 60*30, coerce to POSIXct? >> >> When I tried my method I see that one also needs to add or subtract >> the proper number of seconds from Universal Time to get the output >> formatting correct. (Probably demonstrates that I do not have the >> proper understanding of the right place to employ a TZ >> specification.). >> >> David Winsemius, MD >> West Hartford, CT >> >> ______________________________________________ >> R-help@r-project.org mailing list >> https://stat.ethz.ch/mailman/listinfo/r-help >> PLEASE do read the posting guide >> http://www.R-project.org/posting-guide.html >> and provide commented, minimal, self-contained, reproducible code. >> > > > > -- > Stephen Sefick > ____________________________________ > | Auburn University | > | Department of Biological Sciences | > | 331 Funchess Hall | > | Auburn, Alabama | > | 36849 | > |___________________________________| > | sas0...@auburn.edu | > | http://www.auburn.edu/~sas0025 | > |___________________________________| > > Let's not spend our time and resources thinking about things that are > so little or so large that all they really do for us is puff us up and > make us feel like gods. We are mammals, and have not exhausted the > annoying little problems of being mammals. > > -K. Mullis David Winsemius, MD West Hartford, CT ______________________________________________ R-help@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code. ______________________________________________ R-help@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code.
