What are 'user' and 'system' times measuring in R system.time(exp) output?

Question

I am using system.time(expression) to measure execution time for an R function.

The output I get for the call

system.time(myfunction())
         


        

Answer 1

This is discussed in ?proc.time (system.time() returns an object of class "proc.time"):

Details:

     ‘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.

....and

Value:

....

     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 calling
     process._