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}   ";

```