[R] Getting the month out of my date as a number not characters

[Don MacQueen]

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.
>
>______________________________________________
>R-help at 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.


-- 
--------------------------------------
Don MacQueen
Environmental Protection Department
Lawrence Livermore National Laboratory
Livermore, CA, USA
925-423-1062