Too little detail in one respect: I don't know what different behavior you'd like to see. But here's a way to transform a field while keeping the inside of your loop nice and field-agnostic -- I'll guess that you want to strip the time and display just the date.

use Data::Dumper;

my %field_filter = (creation_date => sub { my $datetime = shift; retur
+n (split ' ', $datetime)[0] } ); 

my @fields = (qw(creation_date a b));

my @hash_ops = ({a => '', b => 2, creation_date => '12/31/2005 12:32:1
+1'},
        {a => 5, b => 0, creation_date => '23/01/2222 13:14:15'});

my @loop_data;
for my $hash_op (@hash_ops) {
    my %row_data;
  foreach my $field (@fields) {
    if ($hash_op->{$field}) {
      $row_data{$field} = exists $field_filter{$field} ? $field_filter
+{$field}->($hash_op->{$field}) : $hash_op->{$field};
    }
    else {
      $row_data{$field} = '-';
    }
  }
  push (@loop_data, \%row_data);
}

print Dumper(\@loop_data)
[download]

This outputs:

$VAR1 = [
          {
            'a' => '-',
            'creation_date' => '12/31/2005',
            'b' => 2
          },
          {
            'a' => 5,
            'creation_date' => '23/01/2222',
            'b' => '-'
          }
        ];
[download]