POSIXlt and daylight savings time

I have a data frame that contains dates, but when I use as.POSIXlt() I lose
the hours on all records. I traced this down to a particuar hour which
causes the issue...
as.POSIXlt('2004-10-31 02:00:00')
[1] "2004-10-31"
as.POSIXlt('2004-10-31 03:00:00')
[1] "2004-10-31 03:00:00"

How do I tell as.POSIXlt() to ignore daylight savings and just convert to a
time as is? I've read about the 'isdst' but it is still unclear what to do.

This is a cleaned up date field that I received so adjusting the date itself
is not possible.

Thanks in advance. 

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a) Don't use POSIXlt in data frames... use POSIXct. POSIXlt is like a data frame of its own, and data frames within data frames lead to surprising results, to say the least.

b) I have had best luck using Sys.setenv( TZ="Etc/GMT+8" ) for US Pacific Standard Time as "local" time for the duration of analysis.

c) Use the format argument if you want consistent results.
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I have a data frame that contains dates, but when I use as.POSIXlt() I
lose
the hours on all records. I traced this down to a particuar hour which
causes the issue...

as.POSIXlt('2004-10-31 02:00:00')
[1] "2004-10-31"
as.POSIXlt('2004-10-31 03:00:00')
[1] "2004-10-31 03:00:00"

How do I tell as.POSIXlt() to ignore daylight savings and just convert
to a
time as is? I've read about the 'isdst' but it is still unclear what to
do.

This is a cleaned up date field that I received so adjusting the date
itself
is not possible.

Thanks in advance. 

--
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http://r.789695.n4.nabble.com/POSIXlt-and-daylight-savings-time-tp4642253.html
Sent from the R help mailing list archive at Nabble.com.

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and provide commented, minimal, self-contained, reproducible code.
I'll rephrase the question...

If you try...

as.POSIXlt('2004-10-31 02:00:00') 

you get 

[1] "2004-10-31" 

What do I need to do to make it return

[1] "2004-10-31 02:00:00" 

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Hello,

Jeff already answered to your question,

as.POSIXlt('2004-10-31 02:00:00', format = "%Y-%m-%d %H:%M:%S")

And in my system and timezone (GMT) I get
as.POSIXlt('2004-10-31 02:00:00')
[1] "2004-10-31 02:00:00"

So Jeff's point (b) should also be followed.

sessionInfo()
R version 2.15.1 (2012-06-22)
Platform: i386-pc-mingw32/i386 (32-bit)

locale:
[1] LC_COLLATE=Portuguese_Portugal.1252 LC_CTYPE=Portuguese_Portugal.1252
[3] LC_MONETARY=Portuguese_Portugal.1252 LC_NUMERIC=C
[5] LC_TIME=Portuguese_Portugal.1252

attached base packages:
[1] stats     graphics  grDevices utils     datasets  methods base

loaded via a namespace (and not attached):
[1] fortunes_1.4-2 tools_2.15.1

Hope this helps,

Rui Barradas

Em 05-09-2012 09:24, pdb escreveu:
I'll rephrase the question...

If you try...

as.POSIXlt('2004-10-31 02:00:00')

you get

[1] "2004-10-31"

What do I need to do to make it return

[1] "2004-10-31 02:00:00"

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View this message in context: http://r.789695.n4.nabble.com/POSIXlt-and-daylight-savings-time-tp4642253p4642272.html
Sent from the R help mailing list archive at Nabble.com.

______________________________________________
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.

as.POSIXlt('2004-10-31 02:00:00')
[1] "2004-10-31"
as.POSIXlt('2004-10-31 03:00:00')
[1] "2004-10-31 03:00:00"

How do I tell as.POSIXlt() to ignore daylight savings and just convert to
a time as is? I've read about the 'isdst' but it is still unclear what to
do.
There *was* no 02:00:00 in your local timezone, so you?re trying to specifiy 
a point in time that just didn?t exist. If you really want to do this, use 
the UTC timezone, by setting the ?tz? argument in as.POSIXct/as.POSIXlt to
UTC (or GMT).
Karl Ove Hufthammer
E-mail: karl at huftis.org
Jabber: huftis at jabber.no