system.time               package:base               R Documentation

CPU Time Used

Description:

     Return CPU (and other) times that `expr' used.

Usage:

     system.time(expr)
     unix.time(expr)

Arguments:

    expr: Valid R expression to be ``timed''

Details:

     `system.time' calls the builtin `proc.time', evaluates `expr', and
     then calls `proc.time' once more, returning the difference between
     the two `proc.time' calls.

     The values returned by the `proc.time' are (on Unix) those
     returned by the C library function `times'(3v).

     `unix.time' is an alias of `system.time', for compatibility
     reasons.

Value:

     A numeric vector of length 5 containing the user cpu, system cpu,
     elapsed, subproc1, subproc2 times. The subproc times are the the
     user and system cpu time used by child processes (and so are
     usually zero).

     The resolution of the times will be system-specific; it is common
     for them to be recorded to of the order of 1/100 second, and
     elapsed time is rounded to the nearest 1/100.

Note:

     It is possible to compile R without support for `system.time',
     when all the values will be `NA'.

See Also:

     `proc.time', `time' which is for time series.

Examples:

     system.time(for(i in 1:50) mad(runif(500)))
     exT <- function(n = 100) {
       # Purpose: Test if system.time works ok;   n: loop size
       system.time(for(i in 1:n) x <- mean(rt(1000, df=4)))
     }
     #-- Try to interrupt one of the following (using Ctrl-C):
     exT()                 #- `1.4' on -O-optimized Ultra1
     system.time(exT())    #~ +/- same

