CODEWITHSUNDEEP
perlhash
user1768233
user1768233

Reputation: 1461

How do I add a new Key,Value pair to a Hash in an array of hash in perl?

I need to add a new key-value pair to the hash entries within an array of hashes. Below is some sample code which does not work (simplified with only one array entry).

The output of the print statement just contains the same one entry.

my @AoH;
push @AoH, { TEST1 => 'testvalue' };
for my $hash (@AoH)
{
    $hash{'TEST2'} = 'testvalue2';
    print Dumper($hash);
}

What am I doing wrong?

Upvotes: 6

Views: 17694

Answers (2)

dms
dms

Reputation: 817

This code looks a little strange, so I am going to assume it was done like that for the purposes of showing it briefly here, but the main thing you need to do to fix your code is change:

$hash{'TEST2'} = 'testvalue2';

to:

$$hash{'TEST2'} = 'testvalue2';

or:

$hash->{'TEST2'} = 'testvalue2';

The extra $ or -> dereferences the hash reference $hash. Since neither is there, it treats $hash{'TEST2'} as a different variable: %hash (not $hash) and assigns testvalue2 to that. You would have gotten a good error message:

Global symbol "%hash" requires explicit package name at - line XX

if you tried to run this code with:

use strict;
use warnings;

at the beginning... which you should always do, so do that every time from now on.

Upvotes: 9

cur4so
cur4so

Reputation: 1820

use strict;
use warnings;
use Data::Dumper;
my @AoH=();
my %data_source_hash=(
TEST1 => 'testvalue1',
TEST2 => 'testvalue2'
);

# adds whole hash as the array element
push @AoH,{ %data_source_hash };

print Dumper(@AoH);
@AoH=();
print "---------------------------\n";

# adds each hash $key, $value pair as an element 

while ( my ($key, $value) = each %data_source_hash )
{
push @AoH, { $key => $value  };
}

print Dumper(@AoH);
@AoH=();
print "---------------------------\n";

# adds extra hash entry to each array element

push @AoH, { TEST1 => 'testvalue'  };
push @AoH, { TEST3 => 'testvalue3'  };
foreach my $el (@AoH)
{
 my $key = 'TEST2';
 $$el{$key} = $data_source_hash{$key};
}
print Dumper(@AoH);

Upvotes: 0

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