> > Suppose I have a two dimensional hash:
> >
> > $name{Adams}{Alice} = 1;
> > $name{Adams}{Bob} = 2;
> > $name{Bull}{Adam} = 3; etc.
> >
> > Given the first key, is there a way to pull out
> > a second key, if I don't care which one?
>
> my ($first) = keys %{$name{Adams}};
>
That answers the question as asked, but the following is
almost certainly more useful:
my %adams = %{$name{Adams}};
print $adams{Alice} . "\n"; # prints 1
print $adams{Bob} . "\n"; # prints 1
then you can work from there.
This works because of the way multidimensional structures
are build... a two dimensional hash is a literal hash of
hashes. This means (confusingly at first (and in my
expression)):
Hash level 1 - keys: Keys of the 1st level
Hash level 1 - values: These store REFERENCES to 2nd level
hashes
Hash level 2 - keys: Keys of the 2nd level
Hash level 2 - values: These store the end values (in this
case)
This is really nice, since it allows you to build tree
structures any way you please. By finding out whether a
node in that tree has a value or a reference you know if
you are on node within the tree, or an end node.
My example code, therefore, dereferences the reference to
the second hash - allowing us to split of a section of the
tree. Apologies due if this makes zero sense.
I suggest studing:
perldoc perlref
Jonathan Paton
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