I am trying to order a series of time data I have stored in a data frame. The format is of:
"%Y-%b"
Which looks like "2009-Sep"etc.
Until now I have managed to find this method:
ds[order(as.Date(ds$yearmonth, format = "%Y-%b")),]
But it only sort by year, and then it moves to alphabetical order regarding the months, giving me an order of 2009-Jan, 2009-Jul, 2009-Jun etc. I am quite puzzled this is not an easy problem to fix.
Please help...
Best Kasper
The as.yearmon() function (and the "yearmon" class) in package zoo is designed for this sort of data:
dat <- c("2009-Sep","2009-Feb","2009-Jan")
require(zoo)
d2 <- as.yearmon(dat, "%Y-%b")
> sort(d2)
[1] "Jan 2009" "Feb 2009" "Sep 2009"
> order(d2)
[1] 3 2 1
> d2[order(d2)]
[1] "Jan 2009" "Feb 2009" "Sep 2009"
You could of course paste0() a day onto each date and coerce to class "Date" via as.Date() but as.yearmon() seems more natural to me:
> as.Date(paste0(dat, "-01"), "%Y-%b-%d")
[1] "2009-09-01" "2009-02-01" "2009-01-01"
Note you can generate that same result by coercing the "yearmon" object to class "as.Date", e.g.:
> as.Date(d2)
[1] "2009-09-01" "2009-02-01" "2009-01-01"