R help - Jul 2009 - Getting the month out of my date as a number not characters

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.

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.

Hi

r-help-bounces at r-project.org napsal dne 02.07.2009 12:40:05:
> 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$date, format = "%m"))
If hf$date is in POSIX format then

format(hf$date,"%m")

shall give you month as a number 01-12. Actually it is a character and you 
need to convert it to numbers by as.numeric.

If it is in different format then depending on how it is actually 
formatted you can use strptime to transform it to POSIX class and then to 
use format to extract only days or months from it.

Regards
Petr


> 
> 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.

Hi

Tim Chatterton <tim.chatterton at uwe.ac.uk> napsal dne 02.07.2009
13:19:46:
>  > Actually it is a character and you  need to convert it to numbers by 
as.numeric
> 
> This is the bit I have problems with - I can easily get it out as 
characters 
> but I cannot work out how to use as.numeric (and had actually given up 
as it 
> seemed to only want to work on numeric fields not character fields).
> 
> Any idea how I do the character to numeric conversion?
> Thanks,
> Tim.
What is the problem with
> format(strptime("20/2/06 11:16:16.683", "%d/%m/%y
%H:%M:%OS"), "%m")
[1] "02"
> as.numeric(format(strptime("20/2/06 11:16:16.683", "%d/%m/%y
%H:%M:%OS"), "%m"))
[1] 2

Regards
Petr

> 
> 
> Petr PIKAL wrote: 
> Hi
> 
> r-help-bounces at r-project.org napsal dne 02.07.2009 12:40:05:
> 
> 
> 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$date, format = "%m"))
> 
> 
> If hf$date is in POSIX format then
> 
> format(hf$date,"%m")
> 
> shall give you month as a number 01-12. Actually it is a character and 
you 
> need to convert it to numbers by as.numeric.
> 
> If it is in different format then depending on how it is actually 
> formatted you can use strptime to transform it to POSIX class and then 
to 
> use format to extract only days or months from it.
> 
> Regards
> Petr
> 
> 
> 
> 
> 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.
> 
> 
> 
> 
> This incoming email to UWE has been independently scanned for viruses by 
> McAfee anti-virus software and none were detected
> 
> 
> -- 
> 
> 
> __________________________________________
> 
> Dr Tim Chatterton
> Senior Research Fellow
> Air Quality Management Resource Centre
> Faculty of Environment and Technology
> University of the West of England
> Frenchay Campus
> Bristol
> BS16 1QY
> 
> Tel: 0117 328 2929
> Fax: 0117 328 3360
> Email: Tim.Chatterton at uwe.ac.uk

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