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Re^2: what is the function should I need to use for trim white spaces ?

by rational_icthus (Sexton)
on Jan 11, 2006 at 19:52 UTC ( #522555=note: print w/replies, xml ) Need Help??


in reply to Re: what is the function should I need to use for trim white spaces ?
in thread what is the function should I need to use for trim white spaces ?

I think the alternation in the s/^\s+|\s+$// version causes significant time costs in large applications. I often work with tab-delimited files containing hundreds of thousands of lines. If I'm tab-splitting these lines and then trimming each one, I'm going to pick the double-regex approach each time. I wrote some quick code that benchmarked the double-regex vs single-regex approach against three strings.
use Benchmark; my @words = ('trim_unneeded',' front trim only','rear trim only ',' + both side trim '); for my $word (@words){ print "Benchmarking $word...\n\n"; timethese(1_000_000, {double => sub{ $word =~ s/^\s+//; $word =~ s +/\s+$//; }, single => sub{ $word =~ s/^\s+|\s+$//; }}) }
The code was run on a Celeron D 2.8 GHz machine running XP with the following results:

'trim_unneeded'
Single Regex: 0.45 seconds
Double Regex: 2.27 seconds

' front trim only'
Single Regex: 0.67 seconds
Double Regex: 2.66 seconds

'rear trim only '
Single Regex: 0.67 seconds
Double Regex: 2.45 seconds

' both side trim '
Single Regex: 0.66 seconds
Double Regex: 2.44 seconds

That's after only 1,000,000 trims. In a 800,000 line file with 50 columns per line, we're talking about 40,000,000 trims. Assuming a linear scale, that means I give up about a minute of processing time per file per run. That's far less than the time it would have taken me to type two regexes. Admittedly, it's a small optimization, and only valid for those who are processing files on the scale that I do, but for most people who end up typing the 'trim regex' often enough to complain about it on perlmonks, it probably applies.
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Re^3: what is the function should I need to use for trim white spaces ?
by phaylon (Curate) on Jan 14, 2006 at 23:14 UTC
    "I think the alternation in the s/^\s+|\s+$// version causes significant time costs in large applications."

    Wait, isn't the single regex faster in your benchmark?

    "Single Regex: 0.45 seconds
    Double Regex: 2.27 seconds"

    Ordinary morality is for ordinary people. -- Aleister Crowley

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