You are still posting in HTML, and it is continuing to impede this
conversation. Learn how to post in plain text before posting again. Gmail
does have this option.
You are not using dput, as previously asked, either. Read the web page I
referenced to learn how to send R data unambiguously.
Your time sequence appears to include 2AM at the spring DST change... no
such point in time exists if you are working with DST, as the clock goes
from 01:59:59 to 03:00:00. I suggest that instead of "EST5EDT" you
specify timezone "Etc/GMT+5" which does not attempt to infer any DST in
the data. "EST" may also work, but there are other timezones in the world
that are referred to by that label, so it may mislead you or not work at
all in the future.
tc <- "3/11/2007 2:00"'
tct <- as.POSIXct( tc, format="%m/%d/%Y %H:%M", tz="Etc/GMT+5")
tct
[1] "2007-03-11 02:00:00 GMT+5"
as.POSIXct( tc, format="%m/%d/%Y %H:%M", tz="EST5EDT")
[1] NA
format(tct, tz="Etc/GMT", usetz=TRUE )
[1] "2007-03-11 07:00:00 GMT"
On Sun, 7 Dec 2014, Alemu Tadesse wrote:
Thank you very much Jeff. Below is the data I used:> Corrected_data
SA_LST SA_GHI_mean
61759 3/11/2007 1:00 0.00000
67517 3/11/2007 2:00 0.00000
70017 3/11/2007 3:00 0.00000
70524 3/11/2007 4:00 0.00000
71061 3/11/2007 5:00 0.00000
71638 3/11/2007 6:00 0.00000
72113 3/11/2007 7:00 20.20873
72629 3/11/2007 8:00 123.14231
73274 3/11/2007 9:00 306.97343
>test1<-as.POSIXct(Corrected_data$SA_LST,format="%m/%d/%Y %H:%M", tz="EST5EDT")
>test1
[1] "2007-03-11 01:00:00 EST" NA "2007-03-11 03:00:00 EDT"
"2007-03-11 04:00:00 EDT"
[5] "2007-03-11 05:00:00 EDT" "2007-03-11 06:00:00 EDT" "2007-03-11 07:00:00 EDT"
"2007-03-11 08:00:00 EDT"
[9] "2007-03-11 09:00:00 EDT"
> format(test1, tz="Etc/GMT", usetz=TRUE )
[1] "2007-03-11 06:00:00 GMT" NA "2007-03-11 07:00:00 GMT"
"2007-03-11 08:00:00 GMT"
[5] "2007-03-11 09:00:00 GMT" "2007-03-11 10:00:00 GMT" "2007-03-11 11:00:00 GMT"
"2007-03-11 12:00:00 GMT"
[9] "2007-03-11 13:00:00 GMT"
>
As you can see the "2007-03-11 02:00:00 EST" is not recognized and returned as
NA. This may be due to DST, which I do not know
how to handle in R.
Best,
Alemu
On Sun, Dec 7, 2014 at 1:59 PM, Jeff Newmiller <jdnew...@dcn.davis.ca.us> wrote:
You have not provided a reproducible example, so anything I say could be
wrong just due to misinterpretation.
Please read [1] for suggestions on making your examples reproducible,
particularly regarding the use of dput to
provide example data. You have also posted in HTML format, which can
cause additional scrambling of communications
on this list.
>From the notation you are using, I would guess that "Corrected_SA_data"
is a data frame containing columns
"date_time" and "TZ" at a minimum. The "date_time" column could be a
vector of class POSIXlt or POSIXct... except
that I cannot reproduce such an object that doesn't print some kind of
timezone indicator in its output. What
version of R are you using? Note that such an object contains a tz
attribute already, so unless you have already
made sure that the date_time column knows about that timezone, they are
probably unrelated to each other.
Note that any POSIXct object is internally represented as a specific
instant of time. The tz attribute is only used
to control how that time will be displayed. For example:
testtime3 <- as.POSIXct( rawtime1, tz="America/New_York" )
format( testtime3, tz="Etc/GMT", usetz=TRUE )
If you want the output to omit the timezone information you can omit the
usetz argument:
format( testtime3, tz="Etc/GMT" )
If you have not yet, you should read [2]. Note that three-letter timezone
indicators (even though they are given in
OUTPUT!) are at best unreliable for use in specifying timezones in R...
read ?timezones.
[1]
http://stackoverflow.com/questions/5963269/how-to-make-a-great-r-reproducible-example
[2] http://www.r-project.org/doc/Rnews/Rnews_2004-1.pdf
On Sun, 7 Dec 2014, Alemu Tadesse wrote:
Dear R users
I am puzzled by the following result from R script. I am trying to convert
local time to UTC time. Time zone is -5, therefore I used the following
approach.
Below is the script.
Corrected_SA_data$date_time[k-1]
[1] "2007-03-11 01:00:00"
Corrected_SA_data$TZ[k-1]
[1] -5
Corrected_SA_data$date_time[k-1]-Corrected_SA_data$TZ[k-1]*3600
[1] "2007-03-11 07:00:00 MDT"
I was expecting this last value to be something like "2007-03-11 06:00:00
UTC"
Please correct me if I ma wrong.
On the other hand I have
Corrected_SA_data$date_time[k]
[1] "2007-03-11 02:00:00"
Corrected_SA_data$TZ[k]
[1] -5
Corrected_SA_data$date_time[k]-Corrected_SA_data$TZ[k]*3600
[1] NA
I am not sure why I am getting NA.
Thank you for your help.
Alemu
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