Beefy Boxes and Bandwidth Generously Provided by pair Networks
Your skill will accomplish
what the force of many cannot

comment on

( #3333=superdoc: print w/replies, xml ) Need Help??
Yes, after I came up with my algorithm, I realized what all the output from GrandFather's code meant. I had thought it was just some sort of cryptic progress meter. :-)

The (reasonably) obvious way to get the longest substring for each pair of input strings would be to run my algorithm using each pair of strings as input rather than the whole list of strings. That's probably more work than GF's method, though. I thought about trying it, but something shiny caught my attention...

Update: but now I've done it. It runs on 20 strings of 1000 characters in something under 10 seconds for me. 100 strings of 1000 characters takes about 4 minutes.

use warnings; use strict; use Time::HiRes; if (@ARGV == 0) { print "Finds longest matching substring between each pair of a set + of test\n"; print "strings in the given file. Pairs of lines are expected with + the first\n"; print "of a pair being the string name and the second the test str +ing."; exit (1); } my $minmatch = 10; my $startTime = [Time::HiRes::gettimeofday ()]; my %strings; while (<>) { chomp(my $label = $_); chomp(my $string = <>); # Compute all substrings @{$strings{$label}} = map [substr($string, $_), $label, $_], 0..(len +gth($string) - $minmatch); } print "Loaded. Generating combos...\n"; my @keys = sort keys %strings; my @best_overall_match = (0); for my $ki1 (0..($#keys - 1)) { for my $ki2 (($ki1 + 1)..$#keys) { my @strings = sort {$a->[0] cmp $b->[0]} @{$strings{$keys[$ki1]}}, + @{$strings{$keys[$ki2]}}; # Now walk through the list. The best match for each string will b +e the # previous or next element in the list that is not from the origin +al substring, # so for each entry, just look for the next one. See how many init +ial letters # match and track the best matches my @matchdata = (0); # (length, index1-into-strings, index2-into-s +trings) for my $i1 (0..($#strings - 1)) { my $i2 = $i1 + 1; ++$i2 while $i2 <= $#strings and $strings[$i2][1] eq $strings[$i +1][1]; next if $i2 > $#strings; my ($common) = map length, ($strings[$i1][0] ^ $strings[$i2][0]) + =~ /^(\0*)/; next if $common < $minmatch; if ($common > $matchdata[0]) { @matchdata = ($common, [$i1, $i2]); } elsif ($common == $matchdata[0]) { push @matchdata, [$i1, $i2]; } } next if $matchdata[0] < $minmatch; if ($matchdata[0] > $best_overall_match[0]) { @best_overall_match = ($matchdata[0]); } if ($matchdata[0] >= $best_overall_match[0]) { push @best_overall_match, map { ["$strings[$_->[0]][1]:$strings[$_->[0]][2]", "$strings[$_->[1 +]][1]:$strings[$_->[1]][2]"] } @matchdata[1..$#matchdata]; } print "$keys[$ki1] and $keys[$ki2]: $matchdata[0] chars\n"; for my $i (@matchdata[1..$#matchdata]) { if ($strings[$i->[0]][1] eq $keys[$ki2]) { @{$i}[0,1] = @{$i}[1,0]; } print "... starting at $strings[$i->[0]][2] and $strings[$i->[1] +][2], respectively.\n"; } } } print "Best overall match: $best_overall_match[0] chars\n"; print "$_->[0] and $_->[1]\n" for (@best_overall_match[1..$#best_o +verall_match]) ; print "Completed in " . Time::HiRes::tv_interval ($startTime) . "\n";

Caution: Contents may have been coded under pressure.

In reply to Re^5: Fast common substring matching by Roy Johnson
in thread Fast common substring matching by GrandFather

Use:  <p> text here (a paragraph) </p>
and:  <code> code here </code>
to format your post; it's "PerlMonks-approved HTML":

  • Are you posting in the right place? Check out Where do I post X? to know for sure.
  • Posts may use any of the Perl Monks Approved HTML tags. Currently these include the following:
    <code> <a> <b> <big> <blockquote> <br /> <dd> <dl> <dt> <em> <font> <h1> <h2> <h3> <h4> <h5> <h6> <hr /> <i> <li> <nbsp> <ol> <p> <small> <strike> <strong> <sub> <sup> <table> <td> <th> <tr> <tt> <u> <ul>
  • Snippets of code should be wrapped in <code> tags not <pre> tags. In fact, <pre> tags should generally be avoided. If they must be used, extreme care should be taken to ensure that their contents do not have long lines (<70 chars), in order to prevent horizontal scrolling (and possible janitor intervention).
  • Want more info? How to link or How to display code and escape characters are good places to start.
Log In?

What's my password?
Create A New User
Domain Nodelet?
and the web crawler heard nothing...

How do I use this? | Other CB clients
Other Users?
Others imbibing at the Monastery: (3)
As of 2023-04-01 13:50 GMT
Find Nodes?
    Voting Booth?

    No recent polls found