Change timezone in a POSIXct object
RDatetimeR Problem Overview
Playing with dateTimes and timezone can be tricky in R.
Here is my question: I want to change the time-zone on a POSIXct object
R) data <- data.frame(x=c(1,2),dateTime=as.POSIXct(c("2010-03-11 03:30:00.432","2010-03-15 03:30:00.432"),format="%Y-%m-%d %H:%M:%S",tz="America/Montreal"))
R) data
x dateTime
1 1 2010-03-11 03:30:00
2 2 2010-03-15 03:30:00
R) str(data)
'data.frame': 2 obs. of 2 variables:
$ x : num 1 2
$ dateTime: POSIXct, format: "2010-03-11 03:30:00" "2010-03-15 03:30:00"
But if I want to change the timezone, the only thing I found is:
R) data$dateTime2 = format(data$dateTime,tz="Europe/Paris")
R) str(data)
'data.frame': 2 obs. of 3 variables:
$ x : num 1 2
$ dateTime : POSIXct, format: "2010-03-11 03:30:00" "2010-03-15 03:30:00"
$ dateTime2: chr "2010-03-11 09:30:00" "2010-03-15 08:30:00"
Or
R) data$dateTime2 = as.POSIXlt(data$dateTime,tz="Europe/Paris")
R) str(data)
'data.frame': 2 obs. of 3 variables:
$ x : num 1 2
$ dateTime : POSIXct, format: "2010-03-11 03:30:00" "2010-03-15 03:30:00"
$ dateTime2: POSIXlt, format: "2010-03-11 09:30:00" "2010-03-15 08:30:00"
God (or somebody on SO) knows why it doesn't work with POSIXct
R) data$dateTime2 = as.POSIXct(data$dateTime,tz="Europe/Paris")
R) str(data)
'data.frame': 2 obs. of 3 variables:
$ x : num 1 2
$ dateTime : POSIXct, format: "2010-03-11 03:30:00" "2010-03-15 03:30:00"
$ dateTime2: POSIXct, format: "2010-03-11 03:30:00" "2010-03-15 03:30:00"
Do I need to convert to character and cast back to POSIXct ?
R Solutions
Solution 1 - R
It doesn't work with POSIXct because base::as.POSIXct.default simply returns x if it's already POSIXct. You can change the timezone via the tzone attribute:
attr(data$dateTime, "tzone") <- "Europe/Paris"
Solution 2 - R
In the lubridate package there is a function with_tz which changes the timezone attribute (effectively what Joshua described).
dttm <- as.POSIXct("2016-01-01 10:10:10", tz = "UTC")
dttm
[1] "2016-01-01 10:10:10 UTC"
Change timezone from UTC to CET
with_tz(dttm, "CET")
[1] "2016-01-01 11:10:10 CET"
Solution 3 - R
As of 7/23/2021. indexTZ is deprecated. tzone is good to use.
tzone(data$dateTime) <- "Europe/Paris"