[Rd] Benchmark code, but avoid printing

[Gábor Csárdi]

Yes, thanks much, this makes a lot of sense.

Well, by "better" what I had in mind was something that is reliably
close to the time needed for printing. Without actually doing the
printing. But I realize this is too much to ask for, and I'll be fine
with /dev/null. Thanks for bringing up the textConnection() issue as
well, especially because I am using textConnection now. /dev/null is a
better option.

Best,
Gabor

On Fri, Jan 2, 2015 at 3:44 PM, Simon Urbanek
<simon.urbanek at r-project.org> wrote:
> On Jan 2, 2015, at 12:02 PM, Gábor Csárdi <csardi.gabor at gmail.com> wrote:
>
>> Dear all,
>>
>> I am trying to benchmark code that occasionally prints on the screen
>> and I want to
>> suppress the printing. Is there an idiom for this?
>>
>> If I do
>>
>> sink(tempfile)
>> microbenchmark(...)
>> sink()
>>
>> then I'll be also measuring the costs of writing to tempfile. I could
>> also sink to /dev/null, which is probably fast, but that is not
>> portable.
>>
>> Is there a better solution? Is writing to a textConnection() better?
>>
>
> Define better - you're just trading off one output code for another - it will be still measuring the cost of the output, obviously, and since the output is part of the code you're profiling it's correctly so. Each output method has different beavior - e.g. text connection can be faster, but it can also trigger additional garbage collection so it will affect results. Example:
>
>> f=textConnection("x", "w")
>> sink(f)
>> m=microbenchmark({ for (i in 1:100) { print("foo"); sum(rnorm(1e3)) } })
>> sink()
>> m
> Unit: milliseconds
>                                                                            expr
>  {     for (i in 1:100) {         print("foo")         sum(rnorm(1000))     } }
>       min       lq     mean   median       uq      max neval
>  12.76462 15.34483 17.85341 17.02435 19.56384 63.09329   100
>> sink("/dev/null")
>> m=microbenchmark({ for (i in 1:100) { print("foo"); sum(rnorm(1e3)) } })
>> sink()
>> m
> Unit: milliseconds
>                                                                            expr
>  {     for (i in 1:100) {         print("foo")         sum(rnorm(1000))     } }
>      min       lq     mean  median       uq      max neval
>  13.0191 13.03601 13.41815 13.0534 13.16496 16.25288   100
>
> As you can see /dev/null is more predictable, because it's straight output, but text connection can be faster in the beginning and becomes progressively slower.
>
> As Henrik said, you're probably best off using simply /dev/null - the only oddball is Windows, and that's a trivial condition on .Platform$OS.type.
>
> Cheers,
> S
>