Re: multiple values for one key in hash

[wade]

in reply to multiple values for one key in hash

How about using a reference to an array. Here's a little ditty that builds the kind of hash for which you're looking and then prints out the results:

use strict;
use warnings;
use diagnostics;
use Data::Dumper;

my %hash;
my $key;
my $value;

my @data = ("foo",1, "bar",2, "foo",3, "baz",4);

while ($key = shift (@data))
{
   $value   = shift (@data);

   # push the value on the array
   push @{$hash{$key}}, $value;
}

print Dumper \%hash;

Note: you have to create the anonymous reference -- you can't just push a value if the key doesn't exist.

Update: apparently you can just push the value.

[moritz]

Note: you have to create the anonymous reference -- you can't just push a value if the key doesn't exist.

In perl you can ;-)

use strict;
use warnings;
use Data::Dumper;

my %hash;
push @{$hash{key}}, 'value';
print Dumper \%hash;
__END__
$VAR1 = {
          'key' => [
                     'value'
                   ]
        };

This nice feature is called "autovivification" and is quite useful most of the time.

[wade]

Son of a gun! You can just push the value. I could have sworn that this didn't work when I tried it at my old job (about 2 years ago). Is this a feature that has happened since then or have I been brain dead all this time?

Thanks, moritz; ++

[dragonchild]

It doesn't work if there was an undef explicitly assigned to the value before. A lot of people get tripped up by this because they just assign undef to something they don't use anymore instead of deleting the key.