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Perl: the Markov chain saw

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I have adopted the following definition of a keyword:


  • Case ignored.
  • Min length: 3, Max length: 20
  • Can include a hyphen or an apostrophe but not at either end (these are stripped). Possessive 's (cat's) also stripped. (can't, won't, hasn't etc. are in the stop list).
  • All other puctuation ignored.
  • Four digit numbers between 1000 and 3000 with an optional trailing s (1960s). Anything else with a number in it is skipped.
  • Skip common words (stop words).


To preserve the apostrophe ’ and ' are replaced with '.

All other HTML entity punctuation is then removed and the HTML decoded. Apart from punctuation it is all Latin1 (I've checked it - at length!).

Update 2
I should have mentioned that the text has already been stripped from an HTML file. (!)
Apologies for any confusion

#!/usr/bin/perl use strict; use warnings; use HTML::Entities; my $config = { minw => 3, maxw => 20, }; my $stop = get_stop(); my $punc = get_punc(); my $text = q| cat&#39;s dogs O&rsquo;Reilly ad-hoc &ldquo;broken&rdquo; hyphen- the and |; my $words_all = {}; # contrived loop to show usage for my $t ($text){ get_word($t); } print "$_\n" for keys %{$words_all}; sub get_word{ my ($text, $file_key) = @_; my ($min, $max) = ($config->{minw}, $config->{maxw}); for ($text){ s/&rsquo;|&#39;/'/g; s/(&#?\w+;)/exists $punc->{$1}?' ':$1/eg; } decode_entities($text); $text =~ s/[^\w'-]/ /g; my @words = split ' ', $text; for (@words){ s/^['-]//g; s/['-]s?$//; next if length() < $min or length() > $max; next if exists $stop->{$_}; next if /\d/ and not /^[12]\d{3}s?$/; next if /--/; push @{$words_all->{$_}}, $file_key; } } sub get_stop{ # sample return { qw( and '' any '' the '' they '' ) }; } sub get_punc{ # sample return { '&rsquo;' => undef, '&lsquo;' => undef, '&rdquo;' => undef, '&ldquo;' => undef, }; } __DATA__ ---------- Capture Output ---------- > "C:\Perl\bin\perl.exe" hyphen cat ad-hoc O'Reilly broken dogs > Terminated with exit code 0.

At the moment the full app is run locally on a copy of the web site.

It's generating 42k words but I'm working on the stop file to try and bring it down.

If this turns out to be fairly stable I'm considering compiling the regexes outside of the loop.

What do you reckon?

winxp, activestate 5.8

Corrected get_stop() sub

In reply to Extracting keywords from HTML by wfsp

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