CODEWITHSUNDEEP
rdatetimetimezone
user3022875
user3022875

Reputation: 9018

Converting incorrect timezone

I have a POSIXct variable that reads 2016-12-15 20:11:29 PST but the PST is incorrect. It should actually read 2016-12-15 20:11:29 GMT

I need to make the time zone correct, GMT, then I need to convert it to New York time

So I am given 2016-12-15 20:11:29 PST. It really should be 2016-12-15 20:11:29 GMT then I need to convert 2016-12-15 20:11:29 GMT to "America/New_York" so the final result will be 16:11:29 America/New_York because new york time is BEHIND GMT time.

I've tried this many ways but can't get it to work. Any ideas?

 p = as.POSIXct("2016-12-15 20:11:29 PST")
 p

********** UPDATE ********* my real code uses a variable and the suggested solutions do not work. see below

     p = as.POSIXct("2016-12-15 20:11:29 PST")
          out = as.POSIXct(p, tz="GMT")
          out
          attr(out,"tzone") <- "America/New_York"
          out

>           out
[1] "2016-12-15 20:11:29 PST"
>           attr(out,"tzone") <- "America/New_York"
>           out
[1] "2016-12-15 23:11:29 EST"  ### this is incorrect

*** This also doe snot work

 p = as.POSIXct(p, usetz=TRUE, tz="GMT")
      (format(p, tz="America/New_York") )

[1] "2016-12-15 23:11:29 EST"
> p = as.POSIXct(p, usetz=TRUE, tz="GMT")
>           (format(p, tz="America/New_York") )
[1] "2016-12-15 23:11:29"

Upvotes: 2

Views: 1028

Answers (2)

IRTFM
IRTFM

Reputation: 263301

I can get you most of the way there but R thinks your are wrong about the time differential:

> p = as.POSIXct("2016-12-15 20:11:29 PST", usetz=TRUE, tz="GMT")
>  p
[1] "2016-12-15 20:11:29 GMT"
> (format(p, tz="America/New_York") )
[1] "2016-12-15 15:11:29"

Response to edit. I'm not seeing the problem. The numeric representation of time in R is always GMT. You can do things at input with parameter to blank out the wrong tz but then your output with format or strftime will simply need to specify a parameter for a different timezone. ( using a variable should have no effect.)

 p = "2016-12-15 20:11:29 PST"
 pp = as.POSIXct(p, usetz=TRUE, tz="GMT")
 pp
[1] "2016-12-15 20:11:29 GMT"

Upvotes: 2

thelatemail
thelatemail

Reputation: 93803

Your issue is that your p is in your system timezone by default:

p = as.POSIXct("2016-12-15 20:11:29 PST")
p
# I'm in Australian Eastern Standard Time, AEST
#[1] "2016-12-15 20:11:29 AEST"
as.numeric(p)
#[1] 1481796689

Convert this local datetime to UTC, which changes the underlying data, by formatting and resetting the timezone to GMT (unless you are already in GMT, then it will do nothing of course):

p2 <- as.POSIXct(format(p),tz="UTC")
p2
#[1] "2016-12-15 20:11:29 UTC"
as.numeric(p2)
#[1] 1481832689
p2 - p
#Time difference of 10 hours
# ...which is the difference between AEST and GMT

Then you can adjust the timezone attribute, which will just alter the display of the date/time object. It does not affect the underlying numeric data:

attr(p2,"tzone") <- "America/New_York"
p2
#[1] "2016-12-15 15:11:29 EST"

as.numeric(p2)
#[1] 1481832689

Upvotes: 1

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