how to count matches

jeanluca has asked for the wisdom of the Perl Monks concerning the following question:

Dear Monks
I thought this was easy, however it turned out I was not able to solve it.
Here is the test code

#! /usr/bin/perl
use strict;
use warnings;

my $n = "ABCDABDIDAOFOOFAA" ;
my $d = ($n =~ /A/g) ;
print "matches $d" ;
[download]

Output is

matches 1
[download]

In this example I try to find out how many A's are present in the string.
Any suggestion what goes wrong here ?

Thnx a lot
LuCa

Comment on how to count matches Select or Download Code

Replies are listed 'Best First'.
Re: how to count matches by merlyn (Sage) on May 04, 2007 at 14:42 UTC
You're using the `$n =~ /A/g` construct in a scalar context. In a scalar context, it moves only one position to the "next" match, and returns the success of the match. If you want to get all the matches, you need to use list context. One ugly way to do that is: `my $d = () = ($n =~ /A/g);` [download] But if you're just counting a single character, use tr/// because it'll be much faster: `my $d = ($n =~ tr/A//);` [download] -- Randal L. Schwartz, Perl hacker	[reply] [d/l] [select]
Re: how to count matches by ferreira (Chaplain) on May 04, 2007 at 14:47 UTC
When you did `my $d = ($n =~ /A/g)` [download] the global match (triggered by /g) was done at scalar context. In this case it finds a single match or fails. So `$d` will return 1 or 0. To do what you want, you need to set a list context and then count the matches. `my $n = "ABCDABDIDAOFOOFAA" ; my @matches = ($n =~ /A/g); my $d = @matches; print "matches $d";` [download] will output "matches 5".	[reply] [d/l] [select]
Re^2: how to count matches by Anonymous Monk on Oct 24, 2015 at 10:42 UTC
doesn't work :(	[reply]
Re: how to count matches by j1n3l0 (Friar) on May 04, 2007 at 15:26 UTC
You can also count all the letters this way: `#!/usr/bin/perl -w use strict; my $string = q<ABCDABDIDAOFOOFAA>; my %count; for (split(//, $string)){$count{$_}++;} print(q<Matches >, $count{A}, "\n");` [download] This way you can choose which letter's count you wish to view ;)	[reply] [d/l]