Perl dereferencing individual elements in array of hash of hash - mysql

Question

I have a structure as below which contains array of hash of hash of hash. I am getting error while dereferencing the values from the hash.
$VAR1 = \{
'2001' => {
'Arunachal Pradesh' => {
'CHANGLANG' => [
{
'wheat' => '2',
'cotton' => '',
'rice' => '1'
}
],
'SUBANSIRI UPPER' => [
{
'wheat' => '',
'cotton' => '1',
'rice' => '2'
}
],
},
'Andhra Pradesh' => {
'CHITTOOR' => [
{
'wheat' => '34',
'cotton' => '14',
'rice' => '27'
}
],
'VIZIANAGARAM' => [
{
'wheat' => '2',
'cotton' => '',
'rice' => '8'
}
],
}
}
};
I am trying to dereferencing individual values such that I can fill these values to a mysql database. But I getting error "Use of uninitialized value $state in concatenation (.) or string" while derefrencing individual value itself. The code is as follows:
while (my ($key, $href) = each(%$stat) ) {
my $state = $stat->{$state_name}; #where the first value is the state name & the second value is the district
print "$state\n";
}
The state name code is as follows:
if ($line =~ m/^State:,(\w+\s\w+),/){
$state_name = $1;
$stat->{$year}->{$state_name} = {};
}
Any other way via which I can get individual values or I need to assign it to another hash and so forth. Thank you.

Answer 1

To step through your structure properly, you need a loop more like this:
while (my ($year, $year_ref) = each(%$stat) )
{
while (my ($state, $state_ref) = each(%$year_ref) )
{
print "year = $year, state = $state\n";
}
}
You can add additional levels of loop below that if you want to iterate through the entire structure to flatten it.
For example, since you have five levels in your structure, and the level just below the last is an array reference:
while (my ($year, $year_ref) = each(%$stat) )
{
while (my ($state, $state_ref) = each(%$year_ref) )
{
while (my ($city, $city_ref) = each(%$state_ref) )
{
foreach my $prod_rec ( #$city_ref )
{
while (my ($prod, $qty) = each(%$prod_rec) )
{
print "year = $year, state = $state, city = $city, prod = $prod, qty = $qty\n";
}
}
}
}
}
(Please forgive me if I guessed wrong naming the level under $state as $city. It is just a guess.)

Answer 2

Learn how to "walk" through the nested hashes/array. Check below code.
#!/usr/bin/perl
use warnings;
use strict;
my $VAR1 = {
'2001' => {
'Arunachal Pradesh' => {
'CHANGLANG' => [
{
'wheat' => '2',
'cotton' => '',
'rice' => '1'
}
],
'SUBANSIRI UPPER' => [
{
'wheat' => '',
'cotton' => '1',
'rice' => '2'
}
],
},
'Andhra Pradesh' => {
'CHITTOOR' => [
{
'wheat' => '34',
'cotton' => '14',
'rice' => '27'
}
],
'VIZIANAGARAM' => [
{
'wheat' => '2',
'cotton' => '',
'rice' => '8'
}
],
}
}
};
foreach my $a (keys %{ $VAR1->{2001} })
{
print $a."\n";
foreach my $b (keys %{ $VAR1->{2001}->{$a} })
{
print "\t".$b."\n";
foreach my $c ( #{ $VAR1->{2001}->{$a}->{$b} })
{
#print $c."\n";
foreach my $d ( keys %{ $c })
{
print "\t\t $d ===> $c->{$d} \n";
}
}
}
}
OutPut:
Arunachal Pradesh
CHANGLANG
rice ===> 1
wheat ===> 2
cotton ===>
SUBANSIRI UPPER
rice ===> 2
wheat ===>
cotton ===> 1
Andhra Pradesh
CHITTOOR
rice ===> 27
wheat ===> 34
cotton ===> 14
VIZIANAGARAM
rice ===> 8
wheat ===> 2
cotton ===>
In above code, I am hitting each and every element of the hash and printing it manually. This way you can capture any element in the hash and then use it later.