On Jan 2, 2015, at 12:02 PM, Gábor Csárdi <csardi.ga...@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
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