difftime {base}  R Documentation 
Time intervals creation, printing, and some arithmetic. The
print()
method calls these “time differences”.
time1  time2
difftime(time1, time2, tz,
units = c("auto", "secs", "mins", "hours",
"days", "weeks"))
as.difftime(tim, format = "%X", units = "auto", tz = "UTC")
## S3 method for class 'difftime'
format(x, ...)
## S3 method for class 'difftime'
units(x)
## S3 replacement method for class 'difftime'
units(x) < value
## S3 method for class 'difftime'
as.double(x, units = "auto", ...)
## Group methods, notably for round(), signif(), floor(),
## ceiling(), trunc(), abs(); called directly, *not* as Math():
## S3 method for class 'difftime'
Math(x, ...)
time1, time2 

tz 
an optional time zone specification to be used for the
conversion, mainly for 
units 
character string. Units in which the results are desired. Can be abbreviated. 
value 
character string. Like 
tim 
character string or numeric value specifying a time interval. 
format 
character specifying the format of 
x 
an object inheriting from class 
... 
arguments to be passed to or from other methods. 
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 groupgeneric (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 datetime objects gives an object of this class,
by calling difftime
with units = "auto"
. Alternatively,
as.difftime()
works on charactercoded 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.
Because R follows POSIX (and almost all computer clocks) in ignoring leap seconds, so do time differences. So in a UTC time zone
z < as.POSIXct(c("20161231 23:59:59", "20170101 00:00:01")) z[2]  z[1]
reports ‘Time difference of 2 secs’ but 3 seconds elapsed while the computer clock advanced by 2 seconds.
If you want the elapsed time interval, you need to add in any leap seconds for yourself.
Units such as "months"
are not possible as they are not of
constant length. To create intervals of months, quarters or years
use seq.Date
or seq.POSIXt
.
(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)