timeZoneConvert: Convert Time Zones

Description

Convert a timeDate object to a new time zone.

Usage

timeZoneConvert(x, zone)

Value

returns the converted timeDate object.

Arguments

x: the time vector object to convert.
zone: the time zone to convert to.

Details

Internally, all timeDate objects are stored as times in GMT with an associated time.zone slot. Conversion to the "local" time zone is done only for the purpose of displaying the timeDate object.

Modifying the time.zone slot directly alters the time zone of the object, but not the time itself. (It represents the same instant in a different part of the world.) When displayed, the time component differs according to the time difference betwwen the time zones before and after the change.

The function timeZoneConvert modifies the time zone and the actual time by the time difference between the new and old time zones. As a result, the printed display of the timeDate object remains the same (other than any displayed time zone information). This is useful when reading in data from a file without specific time zone information (which, by default, is created with a GMT time zone), and then converting it to a different local time zone without changing the printed appearance of the dates and times.

Examples

Run this code

timeDateOptions(time.zone="GMT",
  time.in.format="%m/%d/%Y [%H:%M]",
  time.out.format="%m/%d/%Y %02H:%02M (%Z)")
date1 <- timeDate("3/22/2002 12:00", zone="GMT")
date1 
# 3/22/2002 12:00 (GMT)
date2 <- timeZoneConvert(date1, "PST")
date2 # appears the same as date1, except for zone
# 3/22/2002 12:00 (PST)
date1 - date2 # these times are 8 hours apart

# modifying the time.zone slot does not change
# the actual time, just the display
date3 <- date2
date3@time.zone <- "EST"
date3 # displays as 3 hours later
# 3/22/2002 15:00 (EST)
date2-date3 # but the difference is zero
# 0d 0h 0m 0s 0MS