sorting by date
Jeff Jorgensen <jcjorgensen at wisc.edu> writes:
Hello, I have set up a data.frame and one of the columns contains a date of the form (with slashes as separators): mm/dd/yyyy I would like to use formulas on other columns in the data.frame organized by date, for example: tapply(var1, sort(date), mean)
I don't think that does what I think you think it does!
However, when I try sort(date) it sorts based on the first two entries in the date field: 9/1/2001 9/1/2002 9/1/2003 9/2/2001 ... 5.6 7.5 6.4 7.0 ... Instead of: 9/1/2001 9/2/2001 9/3/2001 9/4/2001 ... 5.6 6.1 7.2 6.8 ... I would greatly appreciate any help in sorting chronologically. Do I need to create separate columns for month, day, and year, and then use order() and then stipulate the hierarchy for which to sort the output? Or, is there some other more efficient way?
You now know why the ISO standard has yyyy-mm-dd ... It's a bit awkward, but I think you need something like pdate <- as.POSIXct(strptime(date,"%m/%d/%Y")) tapply(var1, pdate, mean)
O__ ---- Peter Dalgaard Blegdamsvej 3 c/ /'_ --- Dept. of Biostatistics 2200 Cph. N (*) \(*) -- University of Copenhagen Denmark Ph: (+45) 35327918 ~~~~~~~~~~ - (p.dalgaard at biostat.ku.dk) FAX: (+45) 35327907