Re: [R] diff, POSIXct, POSIXlt, POSIXt

From: jim holtman <jholtman_at_gmail.com>
Date: Sun 23 Jul 2006 - 20:41:40 EST

Try converting to POSIXct:

> str(dts)

'POSIXlt', format: chr [1:10] "2003-04-15" "2003-07-15" "2003-10-15" "2004-04-15" "2004-07-15" "2004-10-15" "2005-04-15" ...
> dts

 [1] "2003-04-15" "2003-07-15" "2003-10-15" "2004-04-15" "2004-07-15" "2004-10-15" "2005-04-15" "2005-07-15"
 [9] "2005-10-15" "2006-04-15"
> dts <- as.POSIXct(dts)
> dts
 [1] "2003-04-15 EDT" "2003-07-15 EDT" "2003-10-15 EDT" "2004-04-15 EDT" "2004-07-15 EDT" "2004-10-15 EDT"
 [7] "2005-04-15 EDT" "2005-07-15 EDT" "2005-10-15 EDT" "2006-04-15 EDT"
> diff(dts)

Time differences of 91, 92, 183, 91, 92, 182, 91, 92, 182 days
>

On 7/23/06, Patrick Giraudoux <patrick.giraudoux@univ-fcomte.fr> wrote:
>
> Dear Listers,
>
> I have encountered a strange problem using diff() and POSIXt:
>
>
> dts<-c("15/4/2003","15/7/2003","15/10/2003","15/04/2004","15/07/2004","15/10/2004","15/4/2005","15/07/2005","15/10/2005","15/4/2006")
> dts <- strptime(dts, "%d/%m/%Y")
> class(dts)
>
> [1] "POSIXt" "POSIXlt"
>
> diff(dts)
>
> Time differences of 7862400, 7948800, 15811200, 7862400, 7948800,
> 15724800, 7862400, 7948800, 0 secs
>
> In this case the result is not the one expected: expressed in seconds
> and not in days, and the difference between the two last dates is not 0.
>
> Now, if one use a vector of 9 dates only (whatever the date removed),
> things come well:
>
> diff(dts[-1])
>
> Time differences of 92, 183, 91, 92, 182, 91, 92, 182 days
>
> Also if one contrains dts to POSIXct
>
>
> dts<-c("15/4/2003","15/7/2003","15/10/2003","15/04/2004","15/07/2004","15/10/2004","15/4/2005","15/07/2005","15/10/2005","15/4/2006")
> dts <- as.POSIXct(strptime(dts, "%d/%m/%Y"))
> diff(dts)
>
> Time differences of 91, 92, 183, 91, 92, 182, 91, 92, 182 days
>
> Any rational in that?
>
> Patrick
>
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>

-- 
Jim Holtman
Cincinnati, OH
+1 513 646 9390

What is the problem you are trying to solve?

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Received on Sun Jul 23 20:59:08 2006

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