Try
hf$hour <- as.POSIXlt(hf$date)$hour
hf$month <- as.POSIXlt(hf$date)$mon+1
To see why, use the man pages to study the structure of POSIXlt objects. Try:
tmp <- strptime("20/2/06 11:16:16.683", "%d/%m/%y %H:%M:%OS")
unclass(tmp)
For example:
tmp <- strptime("20/2/06 11:16:16.683", "%d/%m/%y %H:%M:%OS")
foo <- data.frame(date=c(tmp,tmp+3600), x=1:2)
foo
date x
1 2006-02-20 11:16:16 1
2 2006-02-20 12:16:16 2
foo$hour <- as.POSIXlt(foo$date)$hour
foo$mon <- as.POSIXlt(foo$date)$mon+1
foo
date x hour mon
1 2006-02-20 11:16:16 1 11 2
2 2006-02-20 12:16:16 2 12 2
Just to be thorough, note:
class(tmp)
[1] "POSIXt" "POSIXlt"
class(foo$date)
[1] "POSIXt" "POSIXct"
So strptime() creates objects of class POSIXlt, which are silently
converted to POSIXct when put in a dataframe.
Compare
unclass(tmp)
unclass(foo$date)
-Don
At 11:40 AM +0100 7/2/09, Tim Chatterton wrote:
I have a data frame (hf) that is all set up and the dates are
working fine - however I need to extract the months and hours (2
separate columns) as numbers - however they are coming out as
characters.
I have tried both the following:
hf50$hour= hf50$date
hf50$hour=format(hf50["hour"],"%H")
and
hf$month <- as.POSIXct(strptime(hf$date, format = "%m"))
but they are still coming out as characters.
Any ideas please?
Thanks,
Tim.
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--
--------------------------------------
Don MacQueen
Environmental Protection Department
Lawrence Livermore National Laboratory
Livermore, CA, USA
925-423-1062
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and provide commented, minimal, self-contained, reproducible code.
