proc.time determines how much real and CPU time (in seconds)
the currently running R process has already taken.
An object of class "proc_time" which is a numeric vector of
length 5, containing the user, system, and total elapsed times for the
currently running R process, and the cumulative sum of user and
system times of any child processes spawned by it on which it has
waited. (The print method uses the summary method to
combine the child times with those of the main process.)
The definition of ‘user’ and ‘system’ times is from your
OS. Typically it is something like
The ‘user time’ is the CPU time charged for the execution
of user instructions of the calling process. The ‘system time’
is the CPU time charged for execution by the system on behalf of the
Times of child processes are not available on Windows and will always
be given as NA.
The resolution of the times will be system-specific and on Unix-alikes
times are rounded down to milliseconds. On modern systems they will
be that accurate, but on older systems they might be accurate to 1/100
or 1/60 sec. They are typically available to 10ms on Windows.
proc.time returns five elements for backwards compatibility,
but its print method prints a named vector of
length 3. The first two entries are the total user and system CPU
times of the current R process and any child processes on which it
has waited, and the third entry is the ‘real’ elapsed time
since the process was started.
Becker, R. A., Chambers, J. M. and Wilks, A. R. (1988)
The New S Language.
Wadsworth & Brooks/Cole.
system.time for timing an R expression,
gc.time for how much of the time was spent in garbage