Here's a fairly simple method to measure similarity of strings. Given $one and $two, apply text compression to each and to their concatenation. The ratio of the size of them compressed together to the sum of the separately compressed sizes measures their similarity. The smaller, the closer.

#!/usr/bin/perl

use Compress::Zlib 'compress';

# Usage:   $arrayref = similarity( LIST)
# Returns: AoA reference to string similarity table for LIST
sub similarity {
    my (%single, @ret) = map {$_ => length compress $_} @_;
    for my $this (@_) {
        push @ret, [
            map {
               (length compress $this . $_)
                 / ($single{$this} + $single{$_})
            } @_ 
        ];
    }
    \@ret;
}

my @titles = (
    q(The Last Public Hanging In Old West Virginia - Flatt and Scruggs
+),
    q(Flatt_and_Scruggs__The_Last_Public_Hanging_In_Old_West_Virginia)
+,
    q(Rainy Day Woman Number 12 and 35 - Flatt and Scruggs),
    q(Rainy Day Woman Number Twelve and Thirty-five - Bob Dylan),
);

my $results = similarity @titles;

for my $this (@$results) {
    print pack('A6' x @$this, map {sprintf '%4.3f', $_} @$this), $/;
}

__END__

0.529 0.715 0.784 0.841 
0.708 0.529 0.887 0.870 
0.784 0.863 0.536 0.748 
0.848 0.863 0.739 0.532
[download]

I saw this technique described in a SciAm recently. Will update if I can find out which.

After Compline,
Zaxo