July 08, 2003
Perl Two-Dimensional Hashes
This one's for the search engines...They say that perl doesn't really support two-dimensional hashes, that it instead supports multi-dimensional hashes, or hashes of hashes, through a reference syntax:
$hash->{dimension1}->{dimension2};
But, it actually does support two-dimensional hashes:
$hash->{"dimension1", "dimension2"};
which, I believe, is deprecated from a bygone era. The question is how to loop through the damn thing - how to even isolate the value of "dimension1" from "dimension2".
foreach my $key (keys %$hash) {
print $key; # glommed together
}
That doesn't work. Turns out you need the subscript separator, which is $; . How would you know to look for the definition of the subscript separator? Right. You wouldn't. I lucked out by finding a three-year old article posting on usenet after searching for "2-D Hash". Bleah.
foreach my $key (keys %$hash) {
my ($dimension1, $dimension2) =
(split %;, $key)[0,1];
}