[R] how to order POSIXt objects ?

[jim holtman]

'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
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> --
> 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.
>
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> and provide commented, minimal, self-contained, reproducible code.
>



-- 
Jim Holtman
Data Munger Guru

What is the problem that you are trying to solve?