Printing multi keyed Hash in Perl - perl

Question

I have a perl hash that I am indexing like this:
my %hash;
$hash{'number'}{'even'} = [24, 44, 38, 36];
$hash{'number'}{'odd'} = [23, 43, 37, 35];
When I try to print key names like this:
foreach my $key (keys %hash{'number'})
{
print "Key: $key\n";
}
I get the following error:
Type of arg 1 to keys must be hash (not hash slice) at test.pl
However when I pass the array ref to a function and print it there, it prints the values:
test(\%hash);
sub test
{
my ($hash) = #_;
foreach my $key (keys %{$hash->{'number'}})
{
print "Key: $key\n"; #outputs: even odd
}
}
Can someone please let me know what is going wrong here? Also if I have multi-keyed hash which I have in this case where hash is indexed by both 'number' and 'even' or 'odd' if I do something like this:
foreach my $key (keys %hash)
{
print "First Key: $key\n"; #Outputs number
}
Then will I always get 'number' as the output right and I can never get 'even', 'odd' as outputs, correct? This is just to know good coding practice :)
This is the full code:
sub test
{
my ($hash) = #_;
foreach my $key (keys %{$hash->{'number'}})
{
print "Key: $key\n";
}
}
my %hash;
$hash{'number'}{'even'} = [24, 44, 38, 36];
$hash{'number'}{'odd'} = [23, 43, 37, 35];
test(\%hash);
foreach my $key (keys %hash)
{
print "First Key: $key\n";
}
foreach my $key (keys %hash{'number'})
{
print "Key: $key\n";
}
Thanks,
Newbie

Answer 1

my %hash;
$hash{'number'}{'even'} = [24, 44, 38, 36];
$hash{'number'}{'odd'} = [23, 43, 37, 35];
%hash is a hash whose keys are strings ('number'), and whose values are hash references.
foreach my $key (keys %hash{'number'})
{
print "Key: $key\n";
}
To refer to a value that's part of %hash, you want to write $hash{'number'}, not %hash{'number'}.
But $hash{'number'} is a hash reference, not a hash. To refer to the hash that it refers to, you can write this:
%{$hash{'number'}}
Putting it all together this:
my %hash;
$hash{'number'}{'even'} = [24, 44, 38, 36];
$hash{'number'}{'odd'} = [23, 43, 37, 35];
foreach my $key (keys %{$hash{'number'}}) {
print "Key: $key\n";
}
will produce this output:
Key: even
Key: odd
(possibly not in that order).

Answer 2

You can do something like this:
#!/usr/bin/perl -w
use strict;
use warnings;
my %hash;
$hash{'number'}{'even'} = [24, 44, 38, 36];
$hash{'number'}{'odd'} = [23, 43, 37, 35];
foreach my $i(keys %hash){
print $i;
foreach my $j(keys %{$hash{$i}}){
print "\t".$j."\t";
print join(" ",#{$hash{'number'}{$j}})."\n";
}
}