Where did you get that idea from?  Not from the help page:

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

     'unix.time' is an alias of 'system.time', for compatibility with
     S.

Value:

     A object of class '"proc_time"': see 'proc.time' for details.

and ?proc.time says

     '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.

So, you get measurements of user and system CPU time _and_ elapsed time. E.g.

system.time(Sys.sleep(1.7))
   user  system elapsed
    0.0     0.0     1.7
system.time(Sys.sleep(1.7))[3]
elapsed
   1.69


On Wed, 26 Mar 2008, Faheem Mitha wrote:


Hi,

As far as I can tell, The R function unix.time calculates elapsed CPU
time. Is there a command within R to measure actual elapsed time (I think
this is sometimes referred to as wall time)?

For example, the time command from GNU time calculates the actual elapsed
time, as far as I can tell.

(Please CC me, I'm not subscribed.)
                                                        Thanks, Faheem.

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