insert anonymous hash into anonymous hash for counting in a loop - perl

Question

I'm trying to count starts and stops of some services i keep track of in logs.
I'm not going to past here entire code, but my way of doing hash is this:
I'm passing those starts and stops into anonymous hash .
First I'm creating anonymous hash filled with keys and values (in my case $knot is a key an zeros are values). Next im replaqcing values with another hash.
My code looks like this:
foreach $knot (#knots){
chomp $knot;
$variable = $variable."$knot;0;";
$Services = {split(/;/,$variable)};
}
my $data =
{
Starts=>'0',
Stops=>'0',
};
foreach my $key (keys %$Services) {
$Services->{$key} = $data;
}
print Dumper $Services;
Printing shows:
$VAR1 = {
' knot1' => {
'Stops' => '0',
'Starts' => '0'
},
' knot2' => $VAR1->{' knot1'},
' knot3' => $VAR1->{' knot1'},
' knot4' => $VAR1->{' knot1'},
' knot5' => $VAR1->{' knot1'},
and so on. Is there a better way of doing this? My way if i'm correct is badly written because changing knot1 starts/stops changes every other knot values.

Answer 1

Counting is very simple in Perl, thanks to Autovivification. You can just create anonymous data structures on the fly, like so:
use Data::Dumper;
my %hash = ();
$hash{apple}{green}++;
$hash{apple}{red} ++;
$hash{pear}{yellow}++;
$hash{apple}{green}++;
$hash{apple}{red} ++;
$hash{apple}{green}++;
print Dumper(\%hash);
This will produce the desired structure for counting:
$VAR1 = {
'apple' => {
'green' => 3,
'red' => 2
},
'pear' => {
'yellow' => 1
}
};
This also works in loops using variables (here using a reference to a hash):
my $hash_ref = {};
for my $fruit (qw( apple pear apple peach apple pear )) {
$hash_ref->{$fruit}++;
}
print Dumper($hash_ref);
resulting in:
$VAR1 = {
'peach' => 1,
'pear' => 2,
'apple' => 3
};