Question

I’ll attempt to illustrate this with an example. Take a common example of a Hash of Hashes:

my %HoH = (
    flintstones => {
        lead => "fred",
        pal  => "barney",
    },
    jetsons => {
        lead      => "george",
        wife      => "jane",
        "his boy" => "elroy",
    },
    simpsons => {
        lead => "homer",
        wife => "marge",
        kid  => "bart",
    },
);

For my purposes, I would like to be able to add an unnamed, or anonymous hashes to %HOH. I won’t need (or be able to) define these sub-hashes until runtime. How can I accomplish this with Perl?

Everything I’ve read (and I have read through Perldocs and Google’d already) seems to show examples where all sub-hahes (e.g. “flintstones”, “jetsons”, and “simpsons”) are defined.

What I am doing is attempting to build a parent Hash that will contain sub-hashes with rows from a CSV file:

%TopHash = (
   %Line1 => {
      cell01 => $some_value1a;
      cell02 => $some_value2a;
      cell03 => $some_value3a;
   },
   %Line2 => {
      cell01 => $some_value1b;
      cell02 => $some_value2b;
      cell03 => $some_value3b;
   },
   %Line3 => {
      cell01 => $some_value1c;
      cell02 => $some_value2c;
      cell03 => $some_value3c;
   },
# etc
# etc
# etc

    );

The number of “%LineX” hashes that I need is not known until runtime (because they represent the number of lines in a CSV that is read at runtime).

Any ideas? If it isn’t clear already…I still am trying to wrap my head around Perl hashes.

Answer 1

First you create the hash from the current line you’re parsing

my %lineHash = (
    cell01 => $some_value1a,
    cell02 => $some_value1b,
    cell03 => $some_value1c
);

or create a reference to a hash outright

my $lineHashRef = {
    cell01 => $some_value2a,
    cell02 => $some_value2b,
    cell03 => $some_value2c
};

Then you add it to your overall hash, remembering that nested perl structures just contain references to the other structures.

$topHash{line1} = \%lineHash;
$topHash{line2} = $lineHashRef;

Updated
Example given a loop over an array of data to parse

my %topHash;
foreach my $i (0 .. $#data) {
    my %tempHash;
    // stuff here to parse $data[$i] and populate %tempHash
    $topHash{"line$i"} = \%tempHash;
}