[R] timestamp shifted by hour(s) while mering zoo objects

[Gabor Grothendieck]

Without reproducible code (that means we can copy your code from your
post, paste it into our session and see the same problem that you see)
there is not much that can be said that addresses your specific
situation but in terms of general advice:

- the inappropriate use of time zones is a frequent source of errors
in R for the unwary and you should read R News 4/1 to find out more
about this.

- if after reading that you still want to use POSIXct your best bet is
to set the time zone of your session to GMT and work entirely in GMT:
Sys.setenv(TZ = "GMT")


On Sun, Mar 7, 2010 at 12:20 PM, Keith <kigiokli at gmail.com> wrote:
> Dear R-users,
>
> I have two regular hourly time series data which were recorded in time zone
> GMT+1, and now I would like to merge them together for further analyses.
> Here I used zoo and merge.zoo for my purposes and everything worked fine
> except the timestamp shifted 2 hours after merging which bugs me a little
> bit. Here is the example:
>
> data01
> 00:00:00 01.01.2007, 8.0250
> 01:00:00 01.01.2007, 8.0167
> 02:00:00 01.01.2007, 10.0917
> 03:00:00 01.01.2007, 8.6750
> 04:00:00 01.01.2007, 6.3250
>
> data02
> 00:00:00 01.01.2007, 257.58
> 01:00:00 01.01.2007, 239.92
> 02:00:00 01.01.2007, 234.00
> 03:00:00 01.01.2007, 220.00
> 04:00:00 01.01.2007, 206.92
>
> which are both read into zoo object, data01 and data02, separately by
> setting tz = "GMT+1". However, while merging function is operated, the
> result is
>
> merge.zoo(data01, data02)
>                     data01 data02
> 2007-01-01 02:00:00  8.0250 257.58
> 2007-01-01 03:00:00  8.0167 239.92
> 2007-01-01 04:00:00 10.0917 234.00
> 2007-01-01 05:00:00  8.6750 220.00
> 2007-01-01 06:00:00  6.3250 206.92
>
> which is 2 hours shifted comparing to the original data. I am wondering if
> it's the problem of tz parameter. Hence, I re-read the data by setting tz =
> "GMT", and the merging result is
>
> merge.zoo(data01, data02)
>                     data01 data02
> 2007-01-01 01:00:00  8.0250 257.58
> 2007-01-01 02:00:00  8.0167 239.92
> 2007-01-01 03:00:00 10.0917 234.00
> 2007-01-01 04:00:00  8.6750 220.00
> 2007-01-01 05:00:00  6.3250 206.92
>
> which is 1 hour shifted. I only noticed this but don't know why and how to
> fix it. Does anyone have idea about this issue?
>
> Best regards,
> Keith
>
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