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Re: searching for a string w/ a * in any single position?

by blokhead (Monsignor)
on Oct 05, 2007 at 22:59 UTC ( #642998=note: print w/ replies, xml ) Need Help??

in reply to searching for a string w/ a * in any single position?

Looks like you want to compute the Hamming distance (number of character positions in which they disagree) between two words. Do you really really need a regex, or will another way of matching be ok?

If you're not strongly committed to using a regex, use something like this (probably will do strange things for non-ascii character sets):

sub hamming { my ($x1, $x2) = @_; return -1 if length($x1) != length($x2); (my $xor = $x1 ^ $x2) =~ tr/\x0//cd; } print hamming(@$_), $/ for [qw[ abcdef abccef ]], [qw[ abcdef abc ]], [qw[ abcdef abbbbf ]]; __END__ 1 -1 3
However, you could still cram this hamming function inside of a regex, with some trickery/cheating:
# untested my $target = "abcdef"; my $distance = 1; my $len = length $target; my $qr = qr/ \b(\w{$target})\b (?(??{ hamming($target,$1) < $distance + }) | (?!)) /x
I'm in a bit of a rush at the moment, so my (?(cond)pattern) syntax is probably wrong. Also, it could be optimized greatly to avoid backtracking (say, with (?>pattern) to capture $1). Maybe someone can help me out here with the details, but this should give some idea..


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