CODEWITHSUNDEEP
jsonperl
Fred
Fred

Reputation: 191

Handling hash of hashes decoded by JSON

I have a hash of hashes, $json, received by a perl script from a post method. After decoding the structure with JSON,

use JSON;
my $decode = decode_json($json);

here is the structure from Data::Dumper:

$VAR1 = {
          '11' => {
                    '_by' => 122,
                    '_bx' => 296,
                    '_ay' => 115,
                    '_ax' => 337
                  },
          '21' => {
                    '_by' => 138,
                    '_bx' => 395,
                    '_ay' => 135,
                    '_ax' => 394
                  },
          '7' => {
                   '_by' => 87,
                   '_bx' => 392,
                   '_ay' => 82,
                   '_ax' => 389
                 },
          '17' => {
                    '_by' => 132,
                    '_bx' => 392,
                    '_ay' => 129,
                    '_ax' => 385
                  },
          '2' => {
                   '_by' => 80,
                   '_bx' => 266,
                   '_ay' => 87,
                   '_ax' => 222
                 },
          '22' => {
                    '_by' => 138,
                    '_bx' => 395,
                    '_ay' => 138,
                    '_ax' => 395
                  },
          '1' => {
                   '_by' => 87,
                   '_bx' => 222,
                   '_ay' => 94,
                   '_ax' => 196
                 }
        };

Keys actually go from 0 to 25 (I shorten the structure here for the sake of brevity)

I'm wondering why the following code returns an error:

for (my $i=0; $i<=25; $i++) {
print $decode{$i}{'_bx'};
}

Upvotes: 3

Views: 196

Answers (1)

friedo
friedo

Reputation: 66957

What you've got is a reference to a hash, not a hash, so you need to dereference it. You can access single elements using the -> operator.

for (my $i=0; $i<=25; $i++) {
    print $decode->{$i}{'_bx'};
}

Or much prettier:

for my $i ( 0..25 ) { 
    print $decode->{$i}{_bx};
}

If you want to dereference the entire hash at once, you can use

my %new = %$decode;
for my $i ( 0..25 ) { 
    print $new{$i}{_bx};
}

For more:

Upvotes: 5

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