Re: Data::Rmap to modify an arrayref of arrayrefs

[kcott]

I haven't used Data::Rmap before so others may have better answers. However, the following works and solves your problem.

use strict;
use warnings;

use Data::Rmap qw(:all);

my $initial = [ note => [ shopping => [ 'item' ] ] ];

use Data::Dumper;

# build a list of shopping items ** for reuse **
my @shopping_items;
for my $item qw(bread butter beans) {
    push @shopping_items, [ item => $item ];
}

my ($dump) = rmap_array {
 
  # If we get an arrayref whose first element is 'shopping'
  if ($_->[0] eq 'shopping') {
    # Make the second element the shopping list
    $_->[1] = [ @shopping_items ];
    # No need to drill down any further
    cut($_);
    
  } else {
    # if the arrayrefs first element is not 'shopping'
    # then simply pass it through
    $_;
  }

  } $initial;

warn Dumper($initial, $dump);

[metaperl]

Thanks kcott. I've gone ahead and abstracted htis into a function. Now, I'm going to try to solve it at the level of 'items' instead of at the parent level.

use strict;
use warnings;

use Data::Rmap qw(:all);
use Data::Dumper;

my $initial_lol = [ note => [ shopping => [ item => 'sample' ] ] ];

#  In $initial_lol, the new child of shopping is shopping_items
my $new_lol = newchild($initial_lol, shopping => shopping_items());

warn Dumper($new_lol);



sub newchild {
  my ($lol, $parent_arrayref_label, $new_child)=@_;

  my ($mapresult) = rmap_array {
 

  if ($_->[0] eq $parent_arrayref_label) {
    $_->[1] = $new_child;
    cut($_);
  } else {
    $_;
  }

  } $lol;

  $mapresult;

}

sub shopping_items {
  my @shopping_items;
  for my $item qw(bread butter beans) {
    push @shopping_items, [ item => $item ];
  }
  \@shopping_items;
}

[metaperl]

tada! now I work at the item level instead of it's parent:

use strict;
use warnings;

use Data::Rmap qw(:all);
use Data::Dumper;

my $initial_lol = [ note => [ shopping => [ item => 'sample' ] ] ];

#  In $initial_lol, the new child of shopping is shopping_items
my $new_lol = newnode($initial_lol, item => shopping_items());

warn Dumper($new_lol);



sub newnode {
  my ($lol, $node_label, $new_node)=@_;

  my ($mapresult) = rmap_array {
 

  if ($_->[0] eq $node_label) {
    $_ = shopping_items();
    cut($_);
  } else {
    $_;
  }

  } $lol;

  $mapresult;

}

sub shopping_items {
  my @shopping_items;
  for my $item qw(bread butter beans) {
    push @shopping_items, [ item => $item ];
  }
  \@shopping_items;
}

[metaperl]

My attempt to rewrite the array at the level of the item I wanted to introduced a subtle flaw. I made it clear what data structure I wanted:

[
          'note',
          [
            'shopping',
            
              [
                'item',
                'bread'
              ],
              [
                'item',
                'butter'
              ],
              [
                'item',
                'beans'
              ]
            
          ]
        ];

but then the code above introduces an extra level of array referencing that is not acceptable:

[
          'note',
          [
            'shopping',
            [
              [
                'item',
                'bread'
              ],
              [
                'item',
                'butter'
              ],
              [
                'item',
                'beans'
              ]
            ]
          ]
        ];

it looks like I will have to write the child list at the level of the parent instead of rewriting at the level of the child.