Re: [Rd] strptime(): on Linux system it seems to call system time?

From: Peter Dalgaard <pdalgd_at_gmail.com>
Date: Sat, 20 Mar 2010 18:54:49 +0100

Alexander Peterhansl wrote:
> [I am herewith re-posting this message on R-devel, as it seems to be the
> most appropriate mailing list for this issue.]
>
>
>
> Dear List,
>
>
>

>>From what I understand, strptime() simply converts from one class

> representation to another; i.e., from character to POSIXct/POSIXlt.
>
>
>
> One strange feature of this command running on Linux is that there are
> repeated calls to system time (as was revealed in a trace of system
> calls), which considerably affect performance. These system calls end
> up taking almost 75% of the execution time, and are completely
> unnecessary.
>
>
>
> Code:
>
> ptm <- proc.time()
>
> for (i in 1:100000) strptime("2010-03-10 17:00:00", "%F %H:%M:%S")
>
> (proc.time() -ptm)
>
>
>
> Output on Windows Box (32-bit R 2.9.1 running on Intel X5472 @ 3.0 GHz):
>
> user system elapsed
>
> 1.31 0.02 1.30
>
>
>
> Output on Linux Box (64-bit R 2.10.1 running on Intel Xeon E5520 @
> 2.27GHz):
>
> user system elapsed
>
> 3.33 8.941 12.273
>
>
>
> Any help would be appreciated. Also, if I should turn to a different
> mailing list for this, please let me know.

It seems to be completely system-dependent. On Fedora 9, I see

   user system elapsed
  2.890 0.314 3.374

but on openSUSE 10.3 it is

   user system elapsed
  3.924 6.992 10.917

At any rate, I suspect that this is an issue with the operating system and its C libraries, not with R as such.

-- 
Peter Dalgaard
Center for Statistics, Copenhagen Business School
Phone: (+45)38153501
Email: pd.mes_at_cbs.dk  Priv: PDalgd_at_gmail.com

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