[R] Timings of function execution in R [was Re: R in Industry]

[Frank E Harrell Jr]

Thomas Lumley wrote:
> On 2/9/07, Prof Brian Ripley <ripley at stats.ox.ac.uk> wrote:
>>> The other reason why pmin/pmax are preferable to your functions is that
>>> they are fully generic.  It is not easy to write C code which takes into
>>> account that <, [, [<- and is.na are all generic.  That is not to say that
>>> it is not worth having faster restricted alternatives, as indeed we do
>>> with rep.int and seq.int.
>>>
>>> Anything that uses arithmetic is making strong assumptions about the
>>> inputs.  It ought to be possible to write a fast C version that worked for
>>> atomic vectors (logical, integer, real and character), but is there
>>> any evidence of profiled real problems where speed is an issue?
> 
> 
> I had an example just last month of an MCMC calculation where profiling showed that pmax(x,0) was taking about 30% of the total time.  I used
> 
>      function(x) {z <- x<0; x[z] <- 0; x}
> 
> which was significantly faster. I didn't try the arithmetic solution. Also, I didn't check if a solution like this would still be faster when both arguments are vectors (but there was a recent mailing list thread where someone else did).
> 
> 
>       -thomas

I looked in all the code for the Hmisc and Design packages and didn't 
find a single example where pmin or pmax did not have 2 arguments.  So I 
think it is important to have pmin2 and pmax2.

Frank
> 
> Thomas Lumley			Assoc. Professor, Biostatistics
> tlumley at u.washington.edu	University of Washington, Seattle
-- 
Frank E Harrell Jr   Professor and Chair           School of Medicine
                      Department of Biostatistics   Vanderbilt University