Douglas Douglas - 2 months ago 5
Perl Question

Accessing JSON decoded into a HASH and an array of hash references

Given the following dumper output is there a way to iterate through each hash to list only the items under each

results->id
record? I want to be able to say things like:

print $results{1342}{'domain'};


and have the statement return
testing11.com
as a result.

Would I have to first read through all of
results
array and then use
$results[$counter]{id}
to access the data in there ? I'm not sure how to proceed.

$VAR1 = {
'end_time' => 1466017739,
'options' => {
'hour_offset' => '00',
'timezone' => 'America/New_York'
},
'field_headers' => {
'priority' => 'Priority',
'status' => 'Status',
'assignee_external_id' => 'Assignee external id',
'initially_assigned_at' => 'Initially assigned at'
},
'results' => [
{
'priority' => 'High',
'status' => 'Open',
'domain' => 'testing11.com',
'generated_timestamp' => 1546547669,
'id' => 1342
},
{
'priority' => 'Low',
'status' => 'Open',
'domain' => 'testing22.com',
'generated_timestamp' => 1464567669,
'id' => 7062
},
{
'priority' => 'Low',
'status' => 'Closed',
'domain' => 'testing33.com',
'generated_timestamp' => 1464267669,
'id' => 432
}]
}

Answer

Your dump shows a hashref containing a scalar, two hashrefs and an arrayref. The arrayref has hashrefs for elements. If you want to retrieve specific elements from it, you need to know the index.

$top_level->{results}->[0]->{domain};  # is 'testing11.com'
$top_level->{results}->[0]->{status};  # is 'open'

To iterate through it dereference the array

foreach my $result (@{ $top_level->{results} }) {
    print "$result->{id}\n";
}

Or you can just get values from all results elements for a particular key, say for id

my @ids = map { $_->{id} } @{ $top_level->{results} };
say "@ids";

Prints

1342 7062 432

Note that with nested structures, which contain references, you can also use syntax

$top_level->{results}[0]{domain};  # is 'testing11.com'  

The -> is optional between subscripts, see rule 3. in Using References in perlref.

When the hash keys are strings they should be quoted

$top_level->{'results'}[0]{'domain'};

However, a syntax shortcut allows us to omit quotes on barewords. But if there is anything other than a bareword inside {} it will be interpreted as an expression and evaluated. So if in any doubt use quotes. You want consistent notation throughout.

Resources: Tutorial perlreftut, reference perlref and data structures cookbook, perldsc.


A direct solution is given in stevieb's answer, creating a reverse lookup. Copied here for reference

my $results = $VAR1->{results};

my %by_ip = map {$_->{id} => $_} @$results;

print "$by_ip{1342}->{domain}\n";
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