my $rows = [
            { 'column number 4' => 'data row 1, col 4',
              'column number 2' => 'data row 1, col 2',
              'column number 5' => 'data row 1, col 5',
            },
            { 'column number 4' => 'data row 2, col 4',
              'column number 5' => 'data row 2, col 5',
              'column number 2' => 'data row 2, col 2',
            }
        ];

##</code><code>##

my %rownames;
$rownames{$_} = $_ for sort keys %{@{$rows}[0]};
unshift @$rows, \%rownames;

##</code><code>##

[
          {
            'column number 2' => 'column number 2',
            'column number 5' => 'column number 5',
            'column number 4' => 'column number 4'
          },
# ...