Hi John, The package lubridate is the easiest way to deal with dates.
library(lubridate) frame$groupByWeekNumber <- wday(frame$dt) - 1 # Sun=1, Sat=7 On Mon, Jul 7, 2014 at 11:54 PM, John McKown <john.archie.mck...@gmail.com> wrote: > I have a column, dt, in a data.frame. It is a list of POSIXct objects. > I could use strftime(frame$dt,"%a") to get the day of week as > [sun..sat]. But I need the numeric value in the range of [0..6]. I > can't see a function to do this. I can get it by converting the > POSIXct objects to POSIXlt objects, then extracting the $wday. I don't > know why, but that just doesn't "feel" right to me. What I am actually > trying to do is group my data by Gregorian week (Sunday..Saturday). To > group the data, I am getting the ISO 8601 year and week number using > strftime(dt) with the format of "%G-%V" . But the ISO year&week number > start on Monday, not Sunday. So what I do is: > > dt <- as.POSIXlt(frame$dt); > dt <- dt - dt$wday*86400; # 86400 is seconds in a day > frame$groupByWeekNumber <- strftime(dt,"%G-%V"); > > is there a better way? I have tried my best to find a simpler way. > > -- > There is nothing more pleasant than traveling and meeting new people! > Genghis Khan > > Maranatha! <>< > John McKown > > ______________________________________________ > 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. > [[alternative HTML version deleted]] ______________________________________________ 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.
