Programming Perl, 4th Edition

Creating and Accessing a Two-Dimensional Array

Here’s how to put together a two-dimensional array:

# Assign a list of array references to an array.
@AoA = (
         [ "fred", "barney" ],
         [ "george", "jane", "elroy" ],
         [ "homer", "marge", "bart" ],
);

print $AoA[2][1];   # prints "marge"

The overall list is enclosed by parentheses, not brackets, because you’re assigning a list and not a reference. If you wanted a reference to an array instead, you’d use brackets:

# Create a reference to an array of array references.
$ref_to_AoA = [
    [ "fred", "barney", "pebbles", "bamm bamm", "dino", ],
    [ "homer", "bart", "marge", "maggie", ],
    [ "george", "jane", "elroy", "judy", ],
];

print $ref_to_AoA–>[2][3];   # prints "judy"

Remember that there is an implied –> between every pair of adjacent braces or brackets. Therefore, these two lines:

$AoA[2][3]
$ref_to_AoA–>[2][3]

are equivalent to these two lines:

$AoA[2]–>[3]
$ref_to_AoA–>[2]–>[3]

There is, however, no implied –> before the first pair of brackets, which is why the dereference of $ref_to_AoA requires the initial –>. Also remember that you can count backward from the end of an array with a negative index, so:

$AoA[0][–2]

is the next-to-last element of the first row.