Hello, From my script below, I need a way to determine the number of times each ID appears in my hash. The file contains two IDs on each line: AT1G09700 AT1G01040 AT2G28380 AT1G01040 . . . Each line represents an interaction between the two IDs. I need to determine the number of interactions a particular ID has (called the degree), as well as how many times that degree appears in the entire network (over 60,000 interactions) How could I go about doing this? Subroutines would be very useful. Thank you very much, below is my code. 
#!/local/bin/perl
use strict;
use warnings;

my %hash;
my $holder = "";  #used because it was asked of me

open (EDGES, "<edges.txt") or die "Failed to open edges.txt.\n";
while (<EDGES>){
    chomp ($_);
    if ($_ =~ m/(\S*)(\t)(\S*)/) {
        $hash{$1,$3} = "$holder";
}}

#below isn't needed, just ensures I populated the hash correctly

my $key;                           
   foreach $key (keys %hash){
    print "$key\n";
}

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Update: I should make this a little more clear. On each line contains only two IDs separated by a tab delimiter (notice my match operator). Now each hash has two IDs as the key and a holder variable as the value. I need to determine how many time each ID interacts with (i.e. is in the same key with) another ID. So if it appears in the first position ($1) in 3 keys and the second position ($3) in 2 keys that totals 5 (it can be in the same key as well, i.e. interact with itself). I need to do this for every ID (and have some way to report this in an output file in excel).

In reply to Tallying appearance of a unique string from hash keys by jack_j

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