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;

[download]

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.

--
Wade

Replies are listed 'Best First'.
Re^2: multiple values for one key in hash
by moritz (Cardinal) on May 12, 2008 at 22:12 UTC
    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'
                   ]
        };

    [download]

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

[reply]
[d/l]

      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; ++

      --
      Wade
[reply]
        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.
        My criteria for good software:
        1. Does it work?
        2. Can someone else come in, make a change, and be reasonably certain no bugs were introduced?
[reply]

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