A simple variable count inside array - perl

Question

After working with this code, I am stuck at what I think is a simple error, yet I need outside eyes to see what is wrong.
I used unpack function to divide an array into the following.
#extract =
------MMMMMMMMMMMMMMMMMMMMMMMMMM-M-MMMMMMMM
------SSSSSSSSSSSSSSSSSSSSSSSSSS-S-SSSSSDTA
------TIIIIIIIIIIIIITIIIVVIIIIII-I-IIIIITTT
Apparently, after unpacking into the array, when I try to go into the while loop, #extract shows up completely empty. Any idea as to why this is happening?
print #extract; #<-----------Prints input
my $sum = 0;
my %counter = ();
while (my $column = #extract) {
print #extract; #<------- This extract is completely empty. Should be input
for (my $aa = (split ('', $column))){
$counter{$aa}++;
delete $counter{'-'}; # Don't count -
}
# Sort keys by count descending
my #keys = (sort {$counter{$b} <=> $counter{$a}} keys %counter) [0]; #gives highest letter
for my $key (#keys) {
$sum += $counter{$key};
print OUTPUT "$key $counter{$key} ";

Answer 1

Each line is an array element correct? I don't see in your code where you are checking the individual characters.
Assuming the input that you have shown is a 3 element array containing the line as a string:
#!/usr/bin/perl
use strict;
use warnings;
my #entries;
while(my $line = shift(#extract)){
my %hash;
for my $char(split('', $line)){
if($char =~ /[a-zA-Z]/) { $hash{$char}++ }
}
my $high;
for my $key (keys %hash) {
if(!defined($high)){ $high = $key }
elsif($hash{$high} < $hash{$key}){
$high = $key
}
}
push #entries, {$high => $hash{$high}};
}
Note this empties #extract, if you don't want to do that you'd have to use a for loop like below
for my $i (0 .. $#extract){
#my %hash etc...
}
EDIT:
Changed it so that only the highest number is actually kept

Answer 2

An approach using reduce from List::Util.
#!/usr/bin/perl
use strict;
use warnings;
use List::Util 'reduce';
my #extract = qw/
------MMMMMMMMMMMMMMMMMMMMMMMMMM-M-MMMMMMMM
------SSSSSSSSSSSSSSSSSSSSSSSSSS-S-SSSSSDTA
------TIIIIIIIIIIIIITIIIVVIIIIII-I-IIIIITTT
/;
for (#extract) {
my %count;
tr/a-zA-Z//cd;
for (split //) {
$count{$_}++;
}
my $max = reduce { $count{$a} > $count{$b} ? $a : $b } keys %count;
print "$max $count{$max}\n";
}