Re^2: Skip a row of csv file.


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Re^2: Skip a row of csv file.

by TomDLux (Vicar)

on May 04, 2012 at 18:02 UTC ( [id://968961]=note: print w/replies, xml )

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in reply to Re: Skip a row of csv file.
in thread Skip a row of csv file.

While many people do use regular expressions, I think that's like using an M16 to crack walnuts.

R.E. are the appropriate solution when you have variable components, but testing a constant string is precisely what 'eq' is for.

As Occam said: Entia non sunt multiplicanda praeter necessitatem.

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Re^3: Skip a row of csv file.
by aaron_baugher (Curate) on May 04, 2012 at 23:35 UTC

You make a good point, but I found myself wondering how the combination of substr, length, and eq would compare to a single anchored regex, so I did a benchmark. I'm convinced!

bannor:~/work/perl/monks$ cat 968838.pl
#!/usr/bin/env perl
use Modern::Perl;
use Benchmark qw(:all);

my $str = 'A.SERIAL_NUMBER||abcdefghijklmnopqrstuvwxyz';
my $ss = 'A.SERIAL_NUMBER||';
my $yay;

cmpthese( 10_000_000, {
    'substr' => sub {
        if(substr($str,0,length($ss)) eq $ss ){
            $yay = 1;
        }
    },
    'regex'  => sub {
        if( $str =~ /^\Q$ss\E/ ){
            $yay = 1;
        }
    },
});

bannor:~/work/perl/monks$ perl 968838.pl
            Rate  regex substr
regex  1312336/s     --   -65%
substr 3802281/s   190%     --
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Aaron B.
My Woefully Neglected Blog, where I occasionally mention Perl.

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