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Problem to convert date to number

2 messages · Chris82, David Winsemius

Chris82
# 
Hi R users,

I have a maybe small problem which I cannot solve by myself.

I want to convert 

"chron" "dates" "times"

(04/30/06 11:35:00)


to a number with as.POSIXct.

The Problem is that I can't choose different timezones. I always get "CEST"
and not "UTC" what I need.  

date = as.POSIXct(y,tz="UTC")

"2006-04-30 11:35:00 CEST"

Then I tried to use as.POSIXlt.

date = as.POSIXlt(y,tz="UTC")

"2006-04-30 11:35:00 UTC"

The advantage is I get time in UTC but now the problem is that I can
calculate numbers.

date <- as.double(date)/86400

it is not working with  as.POSIXlt but with as.POSIXct

 
Thanks!

With best regards



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David Winsemius
#
On Apr 6, 2011, at 7:55 AM, Chris82 wrote:

            

      
      
      
    

        
Using the example from help(chron)

 > as.POSIXlt(x)
# chron times are assumed to be UTC but are printed with the current  
local value
[1] "1992-02-27 18:03:20 EST" "1992-02-27 17:29:56 EST"
[3] "1992-01-13 20:03:30 EST" "1992-02-28 13:21:03 EST"
[5] "1992-02-01 11:56:26 EST"
 > as.POSIXlt(x, tz="UTC")
[1] "1992-02-27 23:03:20 UTC" "1992-02-27 22:29:56 UTC"
[3] "1992-01-14 01:03:30 UTC" "1992-02-28 18:21:03 UTC"
[5] "1992-02-01 16:56:26 UTC"
 > as.POSIXlt(x, tz="CEST")  # "not working"
[1] "1992-02-27 23:03:20 UTC" "1992-02-27 22:29:56 UTC"
[3] "1992-01-14 01:03:30 UTC" "1992-02-28 18:21:03 UTC"
[5] "1992-02-01 16:56:26 UTC"

So it makes me wonder if as.POSIXct considers CEST to be a valid tz  
value.

 > as.POSIXlt(x, tz="XYZST")
[1] "1992-02-27 23:03:20 UTC" "1992-02-27 22:29:56 UTC"
[3] "1992-01-14 01:03:30 UTC" "1992-02-28 18:21:03 UTC"
[5] "1992-02-01 16:56:26 UTC"

 > as.POSIXlt(x, tz="EST5EDT")  # where  I am, and seems to be working
[1] "1992-02-27 18:03:20 EST" "1992-02-27 17:29:56 EST"
[3] "1992-01-13 20:03:30 EST" "1992-02-28 13:21:03 EST"
[5] "1992-02-01 11:56:26 EST"

But despite the returned code from Sys.time() that TLA  (EDT) does not  
"work":
 > Sys.time()
[1] "2011-04-06 08:44:01 EDT"
 > as.POSIXlt(x, tz="EDT")
# "EDT" printed as UTC values
[1] "1992-02-27 23:03:20 UTC" "1992-02-27 22:29:56 UTC"
[3] "1992-01-14 01:03:30 UTC" "1992-02-28 18:21:03 UTC"
[5] "1992-02-01 16:56:26 UTC"

But an unambiguous version does return the expected offset. All of  
this can be specific to your system (not provided) and your locale  
setting (also not provided)

 > as.POSIXlt(x, tz="UTC+02")
[1] "1992-02-27 21:03:20 UTC" "1992-02-27 20:29:56 UTC"
[3] "1992-01-13 23:03:30 UTC" "1992-02-28 16:21:03 UTC"
[5] "1992-02-01 14:56:26 UTC"