base (version 3.5.1)

difftime: Time Intervals / Differences

Description

Time intervals creation, printing, and some arithmetic. The print() method calls these “time differences”.

Usage

time1 - time2
difftime(time1, time2, tz,
         units = c("auto", "secs", "mins", "hours",
                   "days", "weeks"))
as.difftime(tim, format = "%X", units = "auto")
# S3 method for difftime
format(x, ...)
# S3 method for difftime
units(x)
# S3 method for difftime
units(x) <- value
# S3 method for difftime
as.double(x, units = "auto", ...)
## Group methods, notably for round(), signif(), floor(),
## ceiling(), trunc(), abs(); called directly, *not* as Math():
# S3 method for difftime
Math(x, …)

Arguments

time1, time2

date-time or date objects.

tz

an optional time zone specification to be used for the conversion, mainly for "POSIXlt" objects.

units

character string. Units in which the results are desired. Can be abbreviated.

value

character string. Like units, except that abbreviations are not allowed.

tim

character string or numeric value specifying a time interval.

format

character specifying the format of tim: see strptime. The default is a locale-specific time format.

x

an object inheriting from class "difftime".

…

arguments to be passed to or from other methods.

Details

Function difftime calculates a difference of two date/time objects and returns an object of class "difftime" with an attribute indicating the units. The Math group method provides round, signif, floor, ceiling, trunc, abs, and sign methods for objects of this class, and there are methods for the group-generic (see Ops) logical and arithmetic operations.

If units = "auto", a suitable set of units is chosen, the largest possible (excluding "weeks") in which all the absolute differences are greater than one.

Subtraction of date-time objects gives an object of this class, by calling difftime with units = "auto". Alternatively, as.difftime() works on character-coded or numeric time intervals; in the latter case, units must be specified, and format has no effect.

Limited arithmetic is available on "difftime" objects: they can be added or subtracted, and multiplied or divided by a numeric vector. In addition, adding or subtracting a numeric vector by a "difftime" object implicitly converts the numeric vector to a "difftime" object with the same units as the "difftime" object. There are methods for mean and sum (via the Summary group generic), and diff via diff.default building on the "difftime" method for arithmetic, notably -.

The units of a "difftime" object can be extracted by the units function, which also has a replacement form. If the units are changed, the numerical value is scaled accordingly. The replacement version keeps attributes such as names and dimensions.

Note that units = "days" means a period of 24 hours, hence takes no account of Daylight Savings Time. Differences in objects of class "Date" are computed as if in the UTC time zone.

The as.double method returns the numeric value expressed in the specified units. Using units = "auto" means the units of the object.

The format method simply formats the numeric value and appends the units as a text string.

See Also

DateTimeClasses.

Examples

# NOT RUN {
(z <- Sys.time() - 3600)
Sys.time() - z                # just over 3600 seconds.

## time interval between release days of R 1.2.2 and 1.2.3.
ISOdate(2001, 4, 26) - ISOdate(2001, 2, 26)

as.difftime(c("0:3:20", "11:23:15"))
as.difftime(c("3:20", "23:15", "2:"), format = "%H:%M") # 3rd gives NA
(z <- as.difftime(c(0,30,60), units = "mins"))
as.numeric(z, units = "secs")
as.numeric(z, units = "hours")
format(z)
# }