indexTZ: Query the TimeZone of an xts object

Description

Get the TimeZone of an xts object.

Usage

indexTZ(x, ...)
tzone(x, ...)
indexTZ(x) <- value
tzone(x) <- value

Arguments

an xts object

value

a valid TZ object

…

unused

Value

A named vector of length one, giving the objects TZ at creation.

Details

As of version 0.6-4 all objects carry the time zone under which they were created in a hidden attribute names .indexTZ.

Going forward from 0.7-4, the TZ variable is now also stored in the index itself, in the tzone attribute. This is to facilitate the transition to removing the xts-specific attributes referenced by indexTZ, indexFormat, and indexClass. These accessor functions will continue to behave the same under the new internals. Additionally, there is a new getter/setter method with tzone and tzone<-.

Internally, all time indexing is converted to POSIXct, seconds since the epoch as defined by a combination of the underlying OS and the TZ variable setting at creation. The current implementation of xts manages time zone information as transparently as possible, delegating all management to R, which is in turn managed in most instances by the underlying operating system.

During printing, and subsetting by time strings the internal POSIX representation is used to identify in human-friendly terms the time at each position.

This is different than previous versions of xts, where the index was stored in its native format (i.e. class).

The ability to create an index using any of the supported timeBased classes (POSIXct, Date, dates, chron, timeDate, yearmon, yearqtr) is managed at the user-interaction point, and the class is merely stored in another hidden attribute names .indexCLASS. This is accessible via the indexClass and indexClass(x)<- functions.

In most cases, all of this makes the subsetting by time strings possible, and also allows for consistent and fast manipulation of the series internally.

Problems may arise when an object that had been created under one TZ (time zone) are used in a session using another TZ. This isn't usually a issue, but when it is a warning is given upon printing or subsetting. This warning may be controlled with options("xts_check_TZ").

Examples

Run this code

# NOT RUN {
x <- xts(1:10, Sys.Date()+1:10)
indexTZ(x)

# same, preferred as of 0.9-1
tzone(x)
str(x)
x
# now set TZ to something different...
# }
# NOT RUN {
Old.TZ <- Sys.getenv("TZ")
Sys.setenv(TZ="America/Chicago")
x
Sys.setenv(TZ=Old.TZ)
# }