[R] Trouble: Time Difference with difftime

[Jeff Newmiller]

Use Date instead of POSIXct. Since your data is already POSIXct you need to 
convert to character and then Date before you use difftime.

 > a <- as.POSIXct("2011-08-02 00:01:00")
 > b <- as.POSIXct("2011-08-01 23:59:00")
 > 
as.Date(as.character(a,format="%Y-%m-%d"))-as.Date(as.character(b,format="%Y-%m-%d"))

On 08/14/2011 06:33 AM, Jim Trabas wrote:
> Hello all!!!
>
> I want to measure the duration of events (given a start and an end time).
> The catch is that I require the output in calender days. This means:
>
> 02-Jan-2011 00:01:00  minus 01-Jan-2011 23:59:00 should be 1 day (although
> the real time difference is only 2 minutes)
>
>
> My data is the following
>
> head(episode.ct)
> [1] "2009-07-13 13:37:20 CEST" "2009-07-14 07:29:20 CEST" "2009-07-14
> 07:51:20 CEST" "2009-07-14 08:45:20 CEST"
> [5] "2009-07-14 09:43:20 CEST" "2009-07-14 10:01:20 CEST"
>
> head(episode.end.ct)
> [1] "2009-07-13 13:47:20 CEST" "2009-07-14 07:49:20 CEST" "2009-07-14
> 08:01:20 CEST" "2009-07-14 08:53:20 CEST"
> [5] "2009-07-14 09:51:20 CEST" "2009-07-14 10:11:20 CEST"
>
> attributes(episode.ct)
> $class
> [1] "POSIXct" "POSIXt"
>
> $tzone
> [1] ""
>
> attributes(episode.end.ct)
> $class
> [1] "POSIXct" "POSIXt"
>
> $tzone
> [1] ""
>
>
> When I try :
>
>> difftime(episode.ct-episode.end.ct)
> I get
>
> Error in as.POSIXct.default(time1) :
>    do not know how to convert 'time1' to class "POSIXct"
>
>
> Why is that? Is difftime what I need?
>
>
> Thank you very much
> JT
>
> --
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>
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