Re: Add array ref to another array ref

[stevieb]

You're working on hashes (hash references, actually), not arrays (array references). There's a significant difference, and push() is used on arrays, which is why you got a collection of hash references within a new array reference. Note that hashes are sometimes referred to as "associative array", which is not the same thing as a normal array.

Here's two ways to do what you want. I created a new hash ref ($hash_c) so I didn't clobber $hash_b before doing the second example. The result is the same though. The first example uses map(), and if both $hash_a and $hash_b both have a key with the same name, the one in $hash_b will be overwritten with $hash_a's value. The second example does a key/value add, but if $hash_b already has a key in $hash_a, we'll just skip it and keep $hash_b's value:

use warnings;
use strict;

use Data::Dumper;

my $data_a = {
    'fullname' => 'Ms Mary Lou',
    'first'    => 'Mary',
    'last'     => 'Lou',
};
        
my $data_b = {
    'house'   => 'main',
    'number'  => '0123',
    'area'    => 'north',
    'code'     => 'zip',
};

my $data_c;
%{ $data_c } = map { $_ => $data_a->{$_} } keys %$data_b, keys %$data_
+a;

for my $k (keys %$data_a){
    $data_b->{$k} = $data_a->{$k} if ! exists $data_b->{$k};
}

print Dumper $data_c;
print Dumper $data_b;

Output:

$VAR1 = {
          'house' => undef,
          'code' => undef,
          'fullname' => 'Ms Mary Lou',
          'last' => 'Lou',
          'area' => undef,
          'first' => 'Mary',
          'number' => undef
        };
$VAR1 = {
          'first' => 'Mary',
          'number' => '0123',
          'house' => 'main',
          'code' => 'zip',
          'fullname' => 'Ms Mary Lou',
          'last' => 'Lou',
          'area' => 'north'
        };

[Fletch]

Trying to push onto a hashref will produce an error so my guess is that $data_b is coming back from wherever as an AoH to begin with.

  DB<1> $a = { qw/ foo bar/ }

  DB<2> $b = { qw/baz quux/ }

  DB<3> x +{ %$a, %$b }
0  HASH(0x7ff1242138f0)
   'baz' => 'quux'
   'foo' => 'bar'
  DB<4> x push @{ $b }, $a
Not an ARRAY reference at (eval 17)[/System/Library/Perl/5.18/perl5db.
+pl:732] line 2.

[Anonymous Monk]

I am getting confused with the data types.
I did a data dumper on $data_b and got this:


$VAR1 = [
          {
            'house'   => 'main',
            'number'  => '0123',
            'area'    => 'north',
            'code'     => 'zip',
          };
         ]


And on $data_a was this:


$VAR1 = {
          'fullname' => 'Ms Mary Lou',
          'first'    => 'Mary',
          'last'     => 'Lou',
        };

[talexb]

When you see the square brackets [], that's an arrayref (a reference to an array). When you see braces {}, that's a hashref (a reference to a hash).

So the first VAR1 that you see is an arrayref with a single element, which is a hashref. The second VAR1 is just a hashref.

[AnomalousMonk]

Please see this, especially the Update.