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

Here is some simple explanations:

Elapsed Time is the time charged to the CPU(s) for the expression.

User Time is the wall clock time. The time that you as a user experienced.

Usually both times are relatively close. But they may vary in some other situations. For example:

• If elapsed time > user time, this means that the CPU is waiting around for some other operations (may be external) to be done.
• If elapsed time < user time, this means that your machine has multiple cores and is able to use them