[R] how to order POSIXt objects ?

[Prof Brian Ripley]

See the help page for order.  It has a similar example, and the 
general solution is to use xtfrm, not unclass.

On Mon, 14 Feb 2011, jim holtman wrote:

> 'unclass' it first(assuming that it is POSIXct)
>
> -unclass(mytime)
>
> On Mon, Feb 14, 2011 at 3:55 AM, JonC <jon_d_cooke at yahoo.co.uk> wrote:
>>
>> I have a problem ordering by descending magnitude a POSIXt object. Can
>> someone help please and let me know how to work around this. My goal is to
>> be able to order my data by DATE and then by descending TIME.
>>
>> I have tried to include as much info as possible below. The problem stems
>> from trying to read in times from a CSV file. I have converted the character
>> time values to a POSIXt object using the STRPTIME function. I would like
>> ideally to sort using the order function as below.
>>
>> test.sort <- order(test$DATE, -test$mytime)
>>
>> However, when I try this I receive the error as below :
>>
>> Error in `-.POSIXt`(test2$mytime) :
>>  unary '-' is not defined for "POSIXt" objects
>>
>> To make this easier to understand I have pasted my example data below with a
>> list of R commands I have used. Any help or assistance would be appreciated.
>>
>>> test2 <- read.csv("C:/Documents and Settings/Jonathan Cooke/My
>>> Documents/Downloads/test2.csv", sep=",")
>>> test2
>>        DATE     TIME
>> 1 18/01/2011 08:00:01
>> 2 18/01/2011 08:10:01
>> 3 18/01/2011 08:20:01
>> 4 18/01/2011 08:30:01
>> 5 19/01/2011 08:00:01
>> 6 19/01/2011 08:10:01
>> 7 19/01/2011 08:20:01
>> 8 19/01/2011 08:30:01
>>
>>> test2$mytime <- strptime(test2$TIME,"%H:%M:%S")
>>> test2$mytime
>> [1] "2011-02-14 08:00:01" "2011-02-14 08:10:01" "2011-02-14 08:20:01"
>> "2011-02-14 08:30:01" "2011-02-14 08:00:01"
>> [6] "2011-02-14 08:10:01" "2011-02-14 08:20:01" "2011-02-14 08:30:01"
>>
>>> test2
>>        DATE     TIME              mytime
>> 1 18/01/2011 08:00:01 2011-02-14 08:00:01
>> 2 18/01/2011 08:10:01 2011-02-14 08:10:01
>> 3 18/01/2011 08:20:01 2011-02-14 08:20:01
>> 4 18/01/2011 08:30:01 2011-02-14 08:30:01
>> 5 19/01/2011 08:00:01 2011-02-14 08:00:01
>> 6 19/01/2011 08:10:01 2011-02-14 08:10:01
>> 7 19/01/2011 08:20:01 2011-02-14 08:20:01
>> 8 19/01/2011 08:30:01 2011-02-14 08:30:01
>>
>>> test2.sort <- order(test2$DATE, -test2$mytime)
>> Error in `-.POSIXt`(test2$mytime) :
>>  unary '-' is not defined for "POSIXt" objects
>>
>> It's at this stage where I have got stuck as I'm new to R and don't yet know
>> a way of getting around this error. Thanks in advance.
>>
>> JonC
>>
>>
>>
>>
>>
>>
>>
>>
>>
>> --
>> View this message in context: http://r.789695.n4.nabble.com/how-to-order-POSIXt-objects-tp3304609p3304609.html
>> Sent from the R help mailing list archive at Nabble.com.
>>
>> ______________________________________________
>> 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.
>>
>
>
>
> -- 
> Jim Holtman
> Data Munger Guru
>
> What is the problem that you are trying to solve?
>
> ______________________________________________
> 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.
>

-- 
Brian D. Ripley,                  ripley at stats.ox.ac.uk
Professor of Applied Statistics,  http://www.stats.ox.ac.uk/~ripley/
University of Oxford,             Tel:  +44 1865 272861 (self)
1 South Parks Road,                     +44 1865 272866 (PA)
Oxford OX1 3TG, UK                Fax:  +44 1865 272595