[R] Which system.time() component to use?

[Ravi Varadhan]

Hi,

The `system.time(expr)' command provide 3 different times for evaluating the expression `expr'; the first two are user and system CPUs and the third one is total elapsed time.  Suppose I want to compare two different computational procedures for performing the same task, which component of `system.time' is most meaningful in the sense that it most accurately reflects the computational effort of the algorithm, and does not depend upon the idiosyncrasies of the operating system.  

I have always been using the first component of `system.time', which is the user CPU.  Should I use the sum of user and system CPU or is the total elapsed time a better measure?  I would appreciate UseR's feedback on this.  

Thanks very much.

Best,
Ravi.
____________________________________________________________________

Ravi Varadhan, Ph.D.
Assistant Professor,
Division of Geriatric Medicine and Gerontology
School of Medicine
Johns Hopkins University

Ph. (410) 502-2619
email: rvaradhan at jhmi.edu