Count matches...with exclusions 1

[CJason]

I'm trying to count the number of "A" characters in a string that are not preceeded AND followed by a "C". So:

$string = "ABCACAB";

should come back with a count of 2 "A" characters. Any ideas/suggestions? I tried:

$count = 0;
$count++ while ($string =~ m/(?<!C)A(?!C)/g);

but count returns with 1, not 2. I guess because it's trying to find matches where A is not preceeded OR followed by a "C"????

 

[KevinADC]

this might need testing to see if it works with more than just your test string:

$count while ($string =~ m/[AB]?(?!<C)A(?!C)[AB]?/g);

------------------------------------------
- Kevin, perl coder unexceptional!

 

[KevinADC]

should be:

$count[red]++[/red] while ($string =~ m/[AB]?(?!<C)A(?!C)[AB]?/g);

------------------------------------------
- Kevin, perl coder unexceptional!

 

[rharsh]

You'll probably want to test this a little better, but it appears to be working:

foreach (qw/ABCACAB ABCAACAB AABCACCAACACABA/) {
	print "$_: " . (() = ([blue][b]m/(?(?<!C)A|A(?!C))/g[/b][/blue])) . "\n";
}

 

[Kirsle]

Kevin

$count++ while ($string =~ m/[AB]?(?!<C)A(?!C)[AB]?/g);

A while loop on a regexp goes through and stops at the end if the "g" tag is on there?

A few times I've wanted to do something like this, but got into infinite loops all the time, and the only solution I could see was to substitute the regexp out of the string one time for each loop, but then sometimes (especially if the regexp is complicated) I make a typo and it still causes an infinite loop.

Cuvou.com | My personal homepage

perl -e '$|=$i=1;print" oo\n<|>\n_|_";x:sleep$|;print"\b",$i++%2?"/":"_";goto x;'

 

[KevinADC]

A while loop on a regexp goes through and stops at the end if the "g" tag is on there?

Yes. Its discussed in perlrequick:

http://perldoc.perl.org/perlrequick.html#More-matching

If you forget the 'g' modifier, a "while" loop could very well never end.

------------------------------------------
- Kevin, perl coder unexceptional!

 

[prex1]

I would do that this way (faster?):

foreach (qw/ABCACAB ABCAACAB AABCACCAACACABA CACAC AAACABCABCCAC/) {
  $count=tr/A/A/-(()=/(?=CAC)/g);
  print"$_: $count\n";
}

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