Thanks, yet again. The Benchmark qw(:hireswallclock) module really shows the difference between the two code segments: 

        my $t0 = Benchmark->new;
        # build TOC
                 
        foreach my $h (split(/\n/, $page)) {
            if ($h =~ m/^={2,3}\s/) {
                push(@toc, $file."\t".$h);
            }
        }
        my $t1 = Benchmark->new;
        my $td = timediff($t1, $t0);
        print "the code took:",timestr($td),"\n";

[download]

and 

        my $t0 = Benchmark->new;
        # build TOC
        push(@toc,
              map(m/^={2,3}\s/ ? $file."\t".$_ : (),
                   split(/\n/, $page) ) );  
        my $t1 = Benchmark->new;
        my $td = timediff($t1, $t0);
        print "the code took:",timestr($td),"\n";

[download]

With the data sets I have, the first one is about a second faster per subset of data. I hope those two segments are similar enough to compare. I don't think I can use substr() because the pieces sought are of variable length and alternations slows it way down. 

        foreach my $h (split(/\n/, $page)) {
            if (substr($h,0,3) eq '== ' 
                 or substr($h,0,4) eq '=== ') {
                push(@toc, $file."\t".$h);
            }
        }

[download]

That adds up to 1.5 seconds.

For what it's worth, the data is by that point markdown text — and a lot of it. The sources are OpenDocument Format word processing files. I got the first 90% of the task done in pure XML using XML::Twig in two afternoons, thanks to advice here. It's the second 90%: dealing with nested lists, cross-references, and individual chapters which is taking even more time. It seems that few are using sections within their ODF files, and so "chapters" end up being all part of the same parent element. Parkinson's law applies as well.

In reply to Re^4: Speed comparison of foreach vs grep + map by mldvx4
in thread Speed comparison of foreach vs grep + map by mldvx4

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