Suppose I have:
my $string = "one.two.three.four";
How should I play with context to get the number of times the pattern found a match (3)? Can this be done using a one-liner?
I tried this:
my ($number) = scalar($string=~/\./gi);
I thought that by putting parentheses around $number, I'd force array context, and by the use of scalar, I'd get the count. However, all I get is 1.
I noticed that if you have an OR condition in your regular expression (eg /(K..K)|(V.AK)/gi ) then the array produced may have undefined elements which are included in the count at the end.
For example:
my $seq = "TSYCSKSNKRCRRKYGDDDDWWRSQYTTYCSCYTGKSGKTKGGDSCDAYYEAYGKSGKTKGGRNNR";
my $regex = '(K..K)|(V.AK)';
my $count = () = $seq =~ /$regex/gi;
print "$count\n";
Gives a value of count of 6.
I found the solution in this post How do I remove all undefs from array?
my $seq = "TSYCSKSNKRCRRKYGDDDDWWRSQYTTYCSCYTGKSGKTKGGDSCDAYYEAYGKSGKTKGGRNNR";
my $regex = '(K..K)|(V.AK)';
my @count = $seq =~ /$regex/gi;
@count = grep defined, @count;
my $count = scalar @count;
print "$count\n";
Which then gives the correct answer of three.
my $count = 0;
my $pos = -1;
while (($pos = index($string, $match, $pos+1)) > -1) {
$count++;
}
checked with Benchmark, it's pretty fast