How can I create multidimensional arrays in Perl?

Question

I am a bit new to Perl, but here is what I want to do:

my @array2d;
while(<FILE>){
  push(@array2d[$i], $_);
}

It doesn't compile since @array2d[$i] is not an array but a scalar value.

How should I declare @array2d as an array of array?

Of course, I have no idea of how many rows I have.

Answer 1

To make an array of arrays, or more accurately an array of arrayrefs, try something like this:

my @array = ();
foreach my $i ( 0 .. 10 ) {
  foreach my $j ( 0 .. 10 ) {
    push @{ $array[$i] }, $j;
  }
}

It pushes the value onto a dereferenced arrayref for you. You should be able to access an entry like this:

print $array[3][2];

Answer 2

Change your "push" line to this:

push(@{$array2d[$i]}, $_);

You are basically making $array2d[$i] an array by surrounding it by the @{}... You are then able to push elements onto this array of array references.

Answer 3

Have a look at perlref and perldsc to see how to make nested data structures, like arrays of arrays and hashes of hashes. Very useful stuff when you're doing Perl.

Answer 4

There's really no difference between what you wrote and this:

@{$array2d[$i]} = <FILE>;

I can only assume you're iterating through files.

To avoid keeping track of a counter, you could do this:

...
push @array2d, [ <FILE> ];
...

That says 1) create a reference to an empty array, 2) storing all lines in FILE, 3) push it onto @array2d.

Answer 5

Another simple way is to use a hash table and use the two array indices to make a hash key:

$two_dimensional_array{"$i $j"} = $val;

Answer 6

If you're just trying to store a file in an array you can also do this:

fopen(FILE,"<somefile.txt");
@array = <FILE>;
close (FILE);