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gryphon has asked for the wisdom of the Perl Monks concerning the following question:

Greetings fellow monks,

After looking over a recent project, I noticed I had written similar code in several sections that effectively did the same thing: Grab data from a database (single query) and build a tree structure from that data. Each time, I was building a structure according to similar rules, so I decided to make a common function.

What I've come up with works, but it has some repeated code. But what concerns me the most is that it's more or less a foreach loop that pushes to an array... which makes me want to rewrite it as a map. Anyway, I've been looking at this for a while and am stuck. I'd like some pointers as to how I could improve the function.

sub tree_data {
  my ( $old_data, $key_name, $next_group, @remaining_keys ) = @_;
  my ( @new_data, $last_key, $build_box );

  foreach ( @{ $old_data } ) {
    if ( $last_key and ( $last_key ne $_->{ $key_name } ) ) {
      push @new_data, {
        $key_name   => $last_key,
        $next_group => ( @remaining_keys )
          ? tree_data( $build_box, @remaining_keys )
          : $build_box,
      };
      undef $build_box;
    }
    $last_key = delete $_->{ $key_name };
    push @{ $build_box }, $_;
  }
  push @new_data, {
    $key_name   => $last_key,
    $next_group => ( @remaining_keys )
      ? tree_data( $build_box, @remaining_keys )
      : $build_box,
  };

  return \@new_data;
}

[download]

What I'm trying to accomplish here is take data from a database call and build a tree from it based on key names. Here's some sample input:

my $input = [
  {
    'team'       => 'A-Team',

    'employee'   => 'Face',
    'work_day'   => '2006-08-28',
    'other_data' => '123456789',
  },
  {
    'team'       => 'A-Team',
    'employee'   => 'Murdock',
    'work_day'   => '2006-08-28',
    'other_data' => '123456789',
  },
  {
    'team'       => 'Military',
    'employee'   => 'Decker',
    'work_day'   => '2006-08-28',
    'other_data' => '123456789',
  },
];

[download]

Here's some sample output:

my $output = [
  {
    'team'      => 'A-Team',
    'employees' => [
      {
          'employee'   => 'Face',
          'work_day'   => '2006-08-28',
          'other_data' => '123456789',
      },
      {
          'employee'   => 'Murdock',
          'work_day'   => '2006-08-28',
          'other_data' => '123456789',
      },
    ],
  },
  {
    'team'      => 'Military',
    'employees' => [
      {
          'employee'   => 'Decker',
          'work_day'   => '2006-08-28',
          'other_data' => '123456789',
      },
    ],
  },
];

[download]

To call the function, I just pass in the data and the key name and sub-group name pairs I want, like this:

# ...to generate the output example from above...
my $output = tree_data( $input, 'team', 'employees' );

# ...to go a little deeper...
my $output = tree_data(
  $input, 'team', 'employees', 'employee', 'work_days'
);

[download]

Going forward, I'm probably going to want to add the ability to pull multiple keys into a particular level, not just a single key; but that's really out of scope for what I'm trying to accomplish right now.

What sort of things should I do to make this function better? Thanks in advance for your suggestions.

gryphon
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