Why does perl "hash of lists" do this? - perl

Question

I have a hash of lists that is not getting populated.
I checked that the block at the end that adds to the hash is in fact being called on input. It should either add a singleton list if the key doesn't exist, or else push to the back of the list (referenced under the right key) if it does.
I understand that the GOTO is ugly, but I've commented it out and it has no effect.
The problem is that when printhits is called, nothing is printed, as if there are no values in the hash. I also tried each (%genomehits), no dice.
THANKS!
#!/usr/bin/perl
use strict;
use warnings;
my $len = 11; # resolution of the peaks
#$ARGV[0] is input file
#$ARGV[1] is call number
# optional -s = spread number from call
# optional -o specify output file name
my $usage = "see arguments";
my $input = shift #ARGV or die $usage;
my $call = shift #ARGV or die $usage;
my $therest = join(" ",#ARGV) . " ";
print "the rest".$therest."\n";
my $spread = 1;
my $output = $input . ".out";
if ($therest =~ /-s\s+(\d+)\s/) {$spread = $1;}
if ($therest =~ /-o\s+(.+)\s/) {$output = $1;}
# initialize master hash
my %genomehits = ();
foreach (split ';', $input) {
my $mygenename = "err_naming";
if ($_ =~ /^(.+)-/) {$mygenename = $1;}
open (INPUT, $_);
my #wiggle = <INPUT>;
&singlegene(\%genomehits, \#wiggle, $mygenename);
close (INPUT);
}
&printhits;
#print %genomehits;
sub printhits {
foreach my $key (%genomehits) {
print "key: $key , values: ";
foreach (#{$genomehits{$key}}) {
print $_ . ";";
}
print "\n";
}
}
sub singlegene {
# let %hash be the mapping hash
# let #mygene be the gene to currently process
# let $mygenename be the name of the gene to currently process
my (%hash) = %{$_[0]};
my (#mygene) = #{$_[1]};
my $mygenename = $_[2];
my $chromosome;
my $leftbound = -2;
my $rightbound = -2;
foreach (#mygene) {
#print "Doing line ". $_ . "\n";
if ($_ =~ "track" or $_ =~ "output" or $_ =~ "#") {next;}
if ($_ =~ "Step") {
if ($_ =~ /chrom=(.+)\s/) {$chromosome = $1;}
if ($_ =~ /span=(\d+)/) {$1 == 1 or die ("don't support span not equal to one, see wig spec")};
$leftbound = -2;
$rightbound = -2;
next;
}
my #line = split /\t/, $_;
my $pos = $line[0];
my $val = $line[-1];
# above threshold for a call
if ($val >= $call) {
# start of range
if ($rightbound != ($pos - 1)) {
$leftbound = $pos;
$rightbound = $pos;
}
# middle of range, increment rightbound
else {
$rightbound = $pos;
}
if (\$_ =~ $mygene[-1]) {goto FORTHELASTONE;}
}
# else reinitialize: not a call
else {
FORTHELASTONE:
# typical case, in an ocean of OFFs
if ($rightbound != ($pos-1)) {
$leftbound = $pos;
}
else {
# register the range
my $range = $rightbound - $leftbound;
for ($spread) {
$leftbound -= $len;
$rightbound += $len;
}
#print $range . "\n";
foreach ($leftbound .. $rightbound) {
my $key = "$chromosome:$_";
if (not defined $hash{$key}) {
$hash{$key} = [$mygenename];
}
else { push #{$hash{$key}}, $mygenename; }
}
}
}
}
}

Answer 1

You are passing a reference to %genomehits to the function singlegene, and then copying it into a new hash when you do my (%hash) = %{$_[0]};. You then add values to %hash which goes away at the end of the function.
To fix it, use the reference directly with arrow notation. E.g.
my $hash = $_[0];
...
$hash->{$key} = yadda yadda;

Answer 2

I think it's this line:
my (%hash) = %{$_[0]};
You're passing in a reference, but this statement is making a copy of your hash. All additions you make in singlegene are then lost when you return.
Leave it as a hash reference and it should work.
PS - Data::Dumper is your friend when large data structures are not behaving as expected. I'd sprinkle a few of these in your code...
use Data::Dumper; print Dumper \%genomehash;