mnlight has asked for the wisdom of the Perl Monks concerning the following question:

I am trying to reference two elements in a hash with one key. 
e.g.
select value[0], value[1], value[1]} from table.
I want value[0] to be the key that refers to value[1] or value[2]

Here is what I tried
while ($values = fetchrow_array()){
my $hash = ($value[0] => $value[1]);
push (@{$hash{$values[0]}}, values[2])
}
foreach $value (keys %has){
print "$hash: @($hash{$value}\n";
}

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this is the error I recieve
Can't use string ("861") as an ARRAY ref while "strict refs" in use

Replies are listed 'Best First'.
Re: 2 elements referenced by one Key
by dragonchild (Archbishop) on Feb 21, 2005 at 16:29 UTC

    First off, kudos for using strict. That saved you from serious issues. 

    my $hash = {
    $value[0] => [ $value[1], $value[2] ],
};

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    Being unknowing, is not the same as being stupid.
    Expressing a contrary opinion, whether to the individual or the group, is more often a sign of deeper thought than of cantankerous belligerence.
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Re: 2 elements referenced by one Key
by Fendaria (Beadle) on Feb 21, 2005 at 16:56 UTC

    Not 100% sure which way you are trying to go.

    If you want multiple keys to one hash value take a look at the CPAN module Tie::Aliashash. It lets you do 

    $hash{ 'foo', 'bar' } = 'baz';

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    If you want multiple values per key take a look at the CPAN module Tie::Hash::Multivalue. It lets you do 

    $hash->{'sample'} = 'one';
$hash->{'sample'} = 'two';
# $hash->{'sample'} now contains ['one','two']

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    among other things.

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Re: 2 elements referenced by one Key
by Tanktalus (Canon) on Feb 21, 2005 at 16:33 UTC

    Two ways off the top of my head: 

    # method 1 - always use an array:
while (my @values = fetchrow_array()){
  my $hash = ($values[0] => [ $values[1] ]);
  push (@{$hash{$values[0]}}, values[2])
}

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    or ... 
    # method 2 - switch scalars to arrays dynamically (good for other
# cases, not so good for yours, here for completeness only)

# rather than a simple push:
if (exists $hash{$values[0]}) {
  if (not ref $hash{$values[0]} or ref $hash{$values[0]} ne 'ARRAY') {
    $hash{$values[0]} = [ $hash{$values[0]} ];
}
push @{$hash{$values[0]}}, $hash{$values[2]};

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    I use the latter in more general cases where I want to default to a single scalar for most cases, and only fall back to arrays when I get the duplication. But the first one makes more sense in the code snippet you gave.

    Update: Off-by-everything error in the inner if in method 2, noted by jdalbec. Replaced "eq" with "ne". (Off-by-everything errors are more common for me than off-by-one errors :->)

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Re: 2 elements referenced by one Key
by jdalbec (Deacon) on Feb 21, 2005 at 16:43 UTC
    Good to see that you're using strict. If you change line 2 to 
    my %hash = ($values[0] => [$values[1]]);

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    then the warning will go away. However, you still have a problem because %hash is local to the while() loop. When you get to the foreach loop it will have gone out of scope and you won't get any output. Try this instead: 
    my %hash;
while ($values = fetchrow_array()){
push (@{$hash{$values[0]}}, values[1]);
push (@{$hash{$values[0]}}, values[2]);
}
foreach $value (keys %hash){
print "\$hash: @{$hash{$value}}\n";
}

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    You may wonder how it's possible to use an undefined value as an array reference. This is a bit of Perl magic called autovivification.
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