R help - Jul 2011 - how to shift a chron timestamp by 6:30 hours

Dear help list,

I have a timestamp in as a chron object:
> (x <- chron(dates = c("12/02/11", "22/11/11"),
+             times = c("07:30:00", "04:00:00"),
+             format = c(dates = "d/m/y", times = "h:m:s")))
[1] (12/02/11 07:30:00) (22/11/11 04:00:00)

Now I want to shift the timestamp by 06:30 (hh:mm) backwards, to get

[1] (12/02/11 01:30:00) (21/11/11 21:30:00)

How can I achieve this? Are there any more detailed examples on
manipulation of chron objects? I have some trouble with this.

Thanks in advance,

Maciej Hoffman-Wecker

Create a difftime object and subtract it from your chron vector.
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Maciej Hoffman-Wecker <Maciej.Hoffman-Wecker@bioskin.de> wrote:

Dear help list,

I have a timestamp in as a chron object:
> (x <- chron(dates = c("12/02/11", "22/11/11"),
+ times = c("07:30:00", "04:00:00"),
+ format = c(dates = "d/m/y", times = "h:m:s")))
[1] (12/02/11 07:30:00) (22/11/11 04:00:00)

Now I want to shift the timestamp by 06:30 (hh:mm) backwards, to get

[1] (12/02/11 01:30:00) (21/11/11 21:30:00)

How can I achieve this? Are there any more detailed examples on
manipulation of chron objects? I have some trouble with this.

Thanks in advance,

Maciej Hoffman-Wecker

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On Jul 28, 2011, at 9:37 AM, Maciej Hoffman-Wecker wrote:
> Dear help list,
>
> I have a timestamp in as a chron object:
>
It would have been courteous to put in:

library(chron)
>> (x <- chron(dates = c("12/02/11", "22/11/11"),
> +             times = c("07:30:00", "04:00:00"),
> +             format = c(dates = "d/m/y", times =
"h:m:s")))
> [1] (12/02/11 07:30:00) (22/11/11 04:00:00)
>
> Now I want to shift the timestamp by 06:30 (hh:mm) backwards, to get
>
> [1] (12/02/11 01:30:00) (21/11/11 21:30:00)
(Your time subtraction is a bit different than R's ... or mine)

 > x - 6.5/24
[1] (12/02/11 01:00:00) (21/11/11 21:30:00)

chron times are represented as days, so 6 1/2 hours is 6.5/24
>
> How can I achieve this? Are there any more detailed examples on
> manipulation of chron objects? I have some trouble with this.
The help page has quite a few examples. I didn't know the answer but  
after reading the help page it was pretty easy to figure out.

David Winsemius, MD
West Hartford, CT

On Thu, Jul 28, 2011 at 9:37 AM, Maciej Hoffman-Wecker
<Maciej.Hoffman-Wecker at bioskin.de> wrote:
> Dear help list,
>
> I have a timestamp in as a chron object:
>
>> (x <- chron(dates = c("12/02/11", "22/11/11"),
> + ? ? ? ? ? ? times = c("07:30:00", "04:00:00"),
> + ? ? ? ? ? ? format = c(dates = "d/m/y", times =
"h:m:s")))
> [1] (12/02/11 07:30:00) (22/11/11 04:00:00)
>
> Now I want to shift the timestamp by 06:30 (hh:mm) backwards, to get
>
> [1] (12/02/11 01:30:00) (21/11/11 21:30:00)
>
Try this:

 x - as.numeric(times("06:30:00"))

If you actually wanted 6 hours behind, which is what the desired
result shown in the post implies, then use "06:00:00" instead.

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