How do I extract an array from a 2D array?

I have a 2D array, and I want to put the first element into a simple array:

use strict;
use warnings;
use Data::Dump;

my @matrix = ([1,2,3], [4], [5,6]);
my @array  = (7,8,9);

my @list = $matrix[0];

print "matrix: " ; dd \@matrix;
print "array:  " ; dd \@array;
print "list:   " ; dd \@list;

print "size of matrix is ", scalar(@matrix), "\n";
print "size of array is  ", scalar(@array),  "\n";
print "size of list is   ", scalar(@list),   "\n";

If I run that, I get output:

matrix: [[1, 2, 3], [4], [5, 6]]
array:  [7, 8, 9]
list:   [[1, 2, 3]]
size of matrix is 3
size of array is  3
size of list is   1

So it seems that list is still a 2-dimensional array. How to I get a one-dimensional array similar to array from the first element of matrix?

You have a reference to an array. You need to dereference it. Change:

my @list = $matrix[0];

to:

my @list = @{ $matrix[0] };

After that change, this is the output:

matrix: [[1, 2, 3], [4], [5, 6]]
array:  [7, 8, 9]
list:   [1, 2, 3]
size of matrix is 3
size of array is  3
size of list is   3

Refer to perldsc