[R] Fwd: strptime() problem?

Gabor Grothendieck ggrothendieck at myway.com
Tue Aug 17 17:57:46 CEST 2004

I am in a different time zone, EDT, on Windows XP and can't
replicate this but you might try reading the latest R News
article on dates and times for some ideas, viz. page 32 of:


In particular, try converting them to chron and then doing 
your manipulations in chron or else convert them from chron to 

   r.asc <- raincida$ts
   r.chron <- chron(substring(r.asc, 1, 10), 
             substring(r.asc, 12, 19), format = c("d/m/y", "h:m:s"))

   r.ct <- as.POSIXct(r.chron)
   format(r.ct, tz="GMT")   # display POSIXct in GMT

Date:   	Tue, 17 Aug 2004 16:25:12 +0200
From:   	javier garcia - CEBAS <rn001 at cebas.csic.es>
To:   	Prof Brian Ripley <ripley at stats.ox.ac.uk>, <r-help at stat.math.ethz.ch>
Subject:   	[R] Fwd: strptime() problem?

Hi all;
I've already send a similar e-mail to the list and Prof. Brian Ripley
answered me but my doubts remain unresolved. Thanks for the clarification,
but perhaps I wasn't clear enough in posting my questions.

I've got a postgres database which I read into R. The first column is
Timestamp with timezone, and my data are already in UTC format. An 'printed'
extract of R character column, resulting from the timestamptz field is:


[2039] "25/03/2000 22:00:00 UTC" "25/03/2000 23:00:00 UTC"
[2041] "26/03/2000 00:00:00 UTC" "26/03/2000 01:00:00 UTC"
[2043] "26/03/2000 02:00:00 UTC" "26/03/2000 03:00:00 UTC"
[2045] "26/03/2000 04:00:00 UTC" "26/03/2000 05:00:00 UTC"

#And I need to convert this character column into POSIXct, for eventual work.
#As I can see in the documentation, the process is to use strptime(), what
#creates an object POSIXlt and doesn't allow to specify that the time zone of
#the data is already UTC; followed by as.POSIXct()

> lluvia.strptime <- strptime(raincida$ts, format="%d/%m/%Y %H:%M:%S")
> lluvia.strptime.POSIXct <- as.POSIXct(lluvia.strptime,tz="GMT")

A "printed" extract is:

[2039] "2000-03-25 22:00:00 GMT" "2000-03-25 23:00:00 GMT"
[2041] "2000-03-26 00:00:00 GMT" "2000-03-26 01:00:00 GMT"
[2043] "2000-03-26 03:00:00 GMT" "2000-03-26 03:00:00 GMT"
[2045] "2000-03-26 04:00:00 GMT" "2000-03-26 05:00:00 GMT"

As we can see, elements [2043] differ. Shouldn't they be similar as the rest
of the other shown elements? I thought this was a bug, but it seems that I've
got and conceptual error.(?). This happens several times in my data, and
produces eventual errors.

Please, how could I resolved this?

Thanks all, and best regards,

Javier G.

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