On 2/9/07, Prof Brian Ripley <ripley@(protected):
>> 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

Thomas Lumley      Assoc. Professor, Biostatistics
tlumley@(protected)

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