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

[Keith]

Thanks Gabor,

Just one comment on the error you received on the Vista machine. I also 
noticed this problem on Windows as well, and found there is no 
specification of "GMT+1" on Windows XP. The closest setting for "GMT+1" 
on windows is "Africa/Lagos", however there is no this problem on *unix 
machine. This is system dependent problem, and I have to admit it's 
somehow annoying.


Gabor Grothendieck wrote:
> On my Vista system I get an error message saying that there is no such
> timezone as GMT+1.
> 
> You may be better off not using time zones and just adjusting the
> times yourself.  You could just use chron and avoid the entire time
> zone problem in the first place.
> 
> In the first of the two approaches below we simply use GMT everywhere
> in the first approach and adjust the result by one hour manually.
> 
> In the second approach we use chron which has no time zones and again
> just adjust the times as we need.
> 
> We have added one hour in both cases here but you may need to add or
> subtract a different number.
> 
> Sys.setenv(TZ = "GMT")
> 
> library(zoo)
> 
> data01.Lines <- "junk
> 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.Lines <- "junk
> 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"
> 
> # POSIXct
> 
> data01 <- read.zoo(textConnection(data01.Lines), sep=",",
> 	format="%H:%M:%S %d.%m.%Y", tz = "GMT", strip.white=TRUE, skip=1)
> 
> data02 <- read.zoo(textConnection(data02.Lines), sep=",",
> 	format="%H:%M:%S %d.%m.%Y", tz = "GMT", strip.white=TRUE, skip=1)
> 
> m <- merge(data01, data02)
> 
> # add 3600 seconds to each time
> time(m) <- time(m) + 3600
> m
> 
> ###
> 
> # chron
> 
> library(chron)
> 
> data01c <- read.zoo(textConnection(data01.Lines), sep=",",
> 	format="%H:%M:%S %d.%m.%Y", FUN = as.chron, strip.white=TRUE, skip=1)
> 
> data02c <- read.zoo(textConnection(data02.Lines), sep=",",
> 	format="%H:%M:%S %d.%m.%Y", FUN = as.chron, strip.white=TRUE, skip=1)
> 
> mc <- merge(data01c, data02c)
> 
> time(mc) <- time(mc) + as.numeric(times("01:00:00"))
> mc
> 
> 
> On Sun, Mar 7, 2010 at 3:36 PM, Keith <kigiokli at gmail.com> wrote:
>> Thanks Gabor,
>>
>> You're right. The problem comes from the environment variable TZ. I just
>> tried the Sys.getenv("TZ") and it's nothing there. After I have set the
>> environment variable TZ as the same as the data, let's say
>> Sys.setenv(TZ="GMT+1"), the problem is gone.
>>
>> In order to complete the problem I've mentioned, here are the data and the
>> code:
>> data01.txt
>> % time[GMT+1:00] Temperature[°C]
>> 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.txt
>> % time[GMT+1:00] Conductance[µS]
>> 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
>>
>> data01 <- read.zoo("data01.txt", sep=",", format="%H:%M:%S %d.%m.%Y",
>> tz="GMT+1", strip.white=TRUE, skip=1)
>>
>> data02 <- read.zoo("data02.txt", sep=",", format="%H:%M:%S %d.%m.%Y",
>> tz="GMT+1", strip.white=TRUE, skip=1)
>>
>> merge.zoo(data01, data02)
>>
>> Besides, thanks for your recommendation, and I'll have a check the R News
>> 4/1.
>>
>> Regards,
>> Keith
>>
>> Gabor Grothendieck wrote:
>>> 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
>>>>
>>>> ______________________________________________
>>>> R-help at r-project.org mailing list
>>>> https://stat.ethz.ch/mailman/listinfo/r-help
>>>> PLEASE do read the posting guide
>>>> http://www.R-project.org/posting-guide.html
>>>> and provide commented, minimal, self-contained, reproducible code.
>>>>
>>
>>