System.time
Gavin Simpson wrote:
On Wed, 2009-02-11 at 18:49 -0600, John Kerpel wrote:
Hi folks!
Does anyone know why I might see something like this after running
system.time?
system.time(svd(Mean_svd_data))
user system elapsed
0 0 0
The data set is tiny and the function returns results instantly, but
shouldn't it still give me a time?
Jim has already suggested why this might be the case. When I'm testing the speed of things like this (that are in and of themselves very quick) for situations where it may matter, I wrap the function call in a call to replicate(): system.time(replicate(1000, svd(Mean_svd_data))) to run it 1000 times, and that allows me to judge how quickly the function executes.
the timethese function in the Benchmark module in perl takes as arguments not only the code to be run, but also the number of replications to be performed. it will complain if the code runs too fast, i.e., if the measured time is too short and is not a reliable estimate. it might be a good idea to have a similar functionality in r (maybe it's already there?), which would basically wrap over system.time and issue a warning when reliable measurement canno tbe made. vQ