You have an array reference. Each element of the array is a hash reference.

So, when you loop, you are doing:

for my $hashRef ( @$my_array_ref ) # Curlies aren't needed here since 
+$my_array_ref is a simple variable name
{
  ...
}
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For each hash ref, you can inspect the contents via: $hashRef->{name} or $hashRef->{type} etc...

It looks like you want to spin through all the data and build a new Hash of Hashes (HoH):

$results->{$transactionType}{$purchasedThing} += $amountSpent
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When looping through the hashes to display, you probably want to sort the keys so that you print in the same order each time.

for my $transactionType (sort keys %$results)
{
  for my $purchasedThings (sort keys %{ $results->{$transactionType} }
+) # Curlies here to mark out what to dereference
  {
    printf("spent \$%5d on %20s using %20s\n",
      $results->{$transactionType}{$purchasedThings},
      $purchasedThings,
      $transactionType,
      );
  }
}
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your explanation makes sense, still having problems, I can print the first item from the array like this:

print $results->[0];
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But running your code is giving me": Not a HASH reference".

It sounds like you're defining $results somewhere that you haven't shown, and making it an array ref.

As I understand it, you want results to be a hash of hashes, so just declare it as my $results; or my $results = {};

You want to loop through the array, printing each item. Since the array is already sorted into groups, you just print a new group header when the value changes:

use feature 'say';
my $type;
for my $entry (@$VAR1) {
        if ( $entry->{type} ne $type ) {
                $type = $entry->{type};
                say $type;
        }
        say "\t$entry->{name} - $entry->{reference}";
}
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This would do it, I could combined all the data into one variable and print at once instead of printing them in the IF, right?

I don't understand your question. If the data is sorted as Loops said, his solution should work for you.

use strict; use warnings;
my $VAR1 = [
   {
     'name' => 'Discount',
     'reference' => '100       ',
     'type' => 'Paper'
   },
   {
     'name' => 'Documents',
     'reference' => '100       ',
     'type' => 'Paper'
   },
   {
     'name' => 'Money',
     'reference' => '340       ',
     'type' => 'Plastic'
   },
   {
     'name' => 'State',
     'reference' => '40        ',
     'type' => 'Cotton'
   },
   {
     'name' => 'Slice',
     'reference' => '30        ',
     'type' => 'Cotton'
   },   {
     'name' => 'Part',
     'reference' => '45        ',
     'type' => 'Cotton'
   },
];

my %results;
$results{$_->{type}}{$_->{name}} += $_->{reference} for (@{$VAR1});

print "Results:\n";
for my $type (keys %results) {
  print "\t$type:\n";
  for my $name (keys %{$results{$type}} ) {
    print "\t\t$name - ".$results{$type}{$name}."\n";
  }
}
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Hi

This is a possible other way to come up with the same output.

use Modern::Perl;

my $data = [
   {
     'name' => 'Discount',
     'reference' => '100       ',
     'type' => 'Paper'
   },
   {
     'name' => 'Documents',
     'reference' => '100       ',
     'type' => 'Paper'
   },
   {
     'name' => 'Money',
     'reference' => '340       ',
     'type' => 'Plastic'
   },
   {
     'name' => 'State',
     'reference' => '40        ',
     'type' => 'Cotton'
   },
   {
     'name' => 'Slice',
     'reference' => '30        ',
     'type' => 'Cotton'
   },   {
     'name' => 'Part',
     'reference' => '45        ',
     'type' => 'Cotton'
   },
];

#recreate a data structure from the existing one,
#but this time the main key is the type.
my %result;
foreach my $elem(@$data) 
{
    my $type = $elem->{type};
    
        #create an array ref for that type
    if (! exists $result{$type} ) 
    {
        $result{$type} = [];
    }

        #store name an reference under that type
    push @{ $result{$type} }, 
        {
            name => $elem->{name},
            reference => $elem->{reference},
        };
}

#loop through the new struct, and for each type,
#print the list of names and references
foreach my $a_type (sort {$a cmp $b} keys %result) 
{
    say $a_type;
    foreach my $a_ref( @{ $result{$a_type} } ) 
    {
        say "\t", $a_ref->{name}, ': ', $a_ref->{reference};
    }

}
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Output

Cotton
    State: 40        
    Slice: 30        
    Part: 45        
Paper
    Discount: 100       
    Documents: 100       
Plastic
    Money: 340
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Cheers.

Arnaud

use strict;
use warnings;

my $array = [
   {
     'name' => 'Discount',
     'reference' => '100       ',
     'type' => 'Paper'
   },
   {
     'name' => 'Documents',
     'reference' => '100       ',
     'type' => 'Paper'
   },
   {
     'name' => 'Money',
     'reference' => '340       ',
     'type' => 'Plastic'
   },
   {
     'name' => 'State',
     'reference' => '40        ',
     'type' => 'Cotton'
   },
   {
     'name' => 'Slice',
     'reference' => '30        ',
     'type' => 'Cotton'
   },   {
     'name' => 'Part',
     'reference' => '45        ',
     'type' => 'Cotton'
   },
];

my %hash;
$hash{$_->{'type'}}{$_->{'name'}} = $_->{'reference'} for @$array;

print "Results:\n";
for my $k1 (sort keys %hash) {
    print "    $k1:\n";
    for my $k2 (sort keys %{$hash{$k1}}) {
        print "        $k2 - $hash{$k1}{$k2}\n";
    }
}
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Results:
    Cotton:
        Part - 45        
        Slice - 30        
        State - 40        
    Paper:
        Discount - 100       
        Documents - 100       
    Plastic:
        Money - 340
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