Thank you very much Jeff. Below is the data I used: > Corrected_data SA_LST SA_GHI_mean 61759 3/11/2007 1:00 0.00000 67517 3/11/2007 2:00 0.00000 70017 3/11/2007 3:00 0.00000 70524 3/11/2007 4:00 0.00000 71061 3/11/2007 5:00 0.00000 71638 3/11/2007 6:00 0.00000 72113 3/11/2007 7:00 20.20873 72629 3/11/2007 8:00 123.14231 73274 3/11/2007 9:00 306.97343
>test1<-as.POSIXct(Corrected_data$SA_LST,format="%m/%d/%Y %H:%M", tz="EST5EDT") >test1 [1] "2007-03-11 01:00:00 EST" NA "2007-03-11 03:00:00 EDT" "2007-03-11 04:00:00 EDT" [5] "2007-03-11 05:00:00 EDT" "2007-03-11 06:00:00 EDT" "2007-03-11 07:00:00 EDT" "2007-03-11 08:00:00 EDT" [9] "2007-03-11 09:00:00 EDT" > format(test1, tz="Etc/GMT", usetz=TRUE ) [1] "2007-03-11 06:00:00 GMT" NA "2007-03-11 07:00:00 GMT" "2007-03-11 08:00:00 GMT" [5] "2007-03-11 09:00:00 GMT" "2007-03-11 10:00:00 GMT" "2007-03-11 11:00:00 GMT" "2007-03-11 12:00:00 GMT" [9] "2007-03-11 13:00:00 GMT" > As you can see the "2007-03-11 02:00:00 EST" is not recognized and returned as NA. This may be due to DST, which I do not know how to handle in R. Best, Alemu On Sun, Dec 7, 2014 at 1:59 PM, Jeff Newmiller <jdnew...@dcn.davis.ca.us> wrote: > You have not provided a reproducible example, so anything I say could be > wrong just due to misinterpretation. Please read [1] for suggestions on > making your examples reproducible, particularly regarding the use of dput > to provide example data. You have also posted in HTML format, which can > cause additional scrambling of communications on this list. > > From the notation you are using, I would guess that "Corrected_SA_data" is > a data frame containing columns "date_time" and "TZ" at a minimum. The > "date_time" column could be a vector of class POSIXlt or POSIXct... except > that I cannot reproduce such an object that doesn't print some kind of > timezone indicator in its output. What version of R are you using? Note > that such an object contains a tz attribute already, so unless you have > already made sure that the date_time column knows about that timezone, they > are probably unrelated to each other. > > Note that any POSIXct object is internally represented as a specific > instant of time. The tz attribute is only used to control how that time > will be displayed. For example: > > testtime3 <- as.POSIXct( rawtime1, tz="America/New_York" ) > format( testtime3, tz="Etc/GMT", usetz=TRUE ) > > If you want the output to omit the timezone information you can omit the > usetz argument: > > format( testtime3, tz="Etc/GMT" ) > > If you have not yet, you should read [2]. Note that three-letter timezone > indicators (even though they are given in OUTPUT!) are at best unreliable > for use in specifying timezones in R... read ?timezones. > > [1] http://stackoverflow.com/questions/5963269/how-to-make- > a-great-r-reproducible-example > [2] http://www.r-project.org/doc/Rnews/Rnews_2004-1.pdf > > > On Sun, 7 Dec 2014, Alemu Tadesse wrote: > > Dear R users >> >> I am puzzled by the following result from R script. I am trying to convert >> local time to UTC time. Time zone is -5, therefore I used the following >> approach. >> >> Below is the script. >> >>> Corrected_SA_data$date_time[k-1] >>> >> [1] "2007-03-11 01:00:00" >> >>> Corrected_SA_data$TZ[k-1] >>> >> [1] -5 >> >>> Corrected_SA_data$date_time[k-1]-Corrected_SA_data$TZ[k-1]*3600 >>> >> [1] "2007-03-11 07:00:00 MDT" >> >> I was expecting this last value to be something like "2007-03-11 06:00:00 >> UTC" >> >> Please correct me if I ma wrong. >> >> On the other hand I have >> >>> Corrected_SA_data$date_time[k] >>> >> [1] "2007-03-11 02:00:00" >> >>> Corrected_SA_data$TZ[k] >>> >> [1] -5 >> >>> Corrected_SA_data$date_time[k]-Corrected_SA_data$TZ[k]*3600 >>> >> [1] NA >> >> I am not sure why I am getting NA. >> >> Thank you for your help. >> >> Alemu >> >> [[alternative HTML version deleted]] >> >> ______________________________________________ >> R-help@r-project.org mailing list -- To UNSUBSCRIBE and more, see >> 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. >> >> > ------------------------------------------------------------ > --------------- > Jeff Newmiller The ..... ..... Go Live... > DCN:<jdnew...@dcn.davis.ca.us> Basics: ##.#. ##.#. Live > Go... > Live: OO#.. Dead: OO#.. Playing > Research Engineer (Solar/Batteries O.O#. #.O#. with > /Software/Embedded Controllers) .OO#. .OO#. rocks...1k > ------------------------------------------------------------ > --------------- > [[alternative HTML version deleted]] ______________________________________________ R-help@r-project.org mailing list -- To UNSUBSCRIBE and more, see 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.