Perl 2x2 array addition using Subroutines and Reference - perl

Question

My question in Perl is:
Define 2x2 arrays using anonymous lists. Pass the arrays to a subroutine and add them together. Return a reference to sum array and print the values from the main part of the program.
My script is:
#!/usr/bin/perl
use strict;
use warnings;
my #array = ([1,2],[4,5]);
my $refarray = \#array;
print sumarray($refarray);
sub sumarray
{
$refarray = shift;
foreach (#{$refarray})
{
$refarray = ($refarray[0]->[0]+$refarray[1]->[0],$refarray[0]->[1]+$refarray[1]->[1]);
}
return $refarray;
}
Where am I going wrong? Please help. Thanks in advance.
I am getting the output as 0.
If I use use strict; and use warnings; I will get the error message as
Global symbol "#refarray" requires explicit package name at line 23.
Global symbol "#refarray" requires explicit package name at line 23.
Global symbol "#refarray" requires explicit package name at line 23.
Global symbol "#refarray" requires explicit package name at line 23.
Execution aborted due to compilation errors.

Answer 1

Few problems with your code: -
First, in your for-loop, you are modifying your reference $refarray which you should not do.
Second, $refarray[0]->[0] will not compile. Since $refarray is a reference to an array, you should either use its 1st element using arrow: - $refarray->[0][0], or you need to de-reference it before using the way you are using: - $$refarray[0]->[0].
Having said that, I think you should replace your subroutine with this one: -
use strict;
use warnings;
my #array = ([1,2],[4,5]);
my $refarray = \#array;
my $sum = sumarray($refarray);
print $sum->[0], $sum->[1];
sub sumarray {
my $ref = shift;
return [$ref->[0][0] + $ref->[1][0], $ref->[0][1] + $ref->[1][1]];
}
OUTPUT: -
5 7

Answer 2

Try this:
#!/usr/bin/perl -w
my $r = sumarray([1,2],[3,4]);
print $r->[0], " ", $r->[1], "\n";
sub sumarray {
my ($a, $b) = #_;
return [
$a->[0]+$b->[0],
$a->[1]+$b->[1]
];
}

Answer 3

It could be expressed very simply with a combination of the list operations sum (from the core module List::Util) and map.
Code
#!/usr/bin/env perl
use strict;
use warnings;
use feature 'say';
use List::Util 'sum';
sub sum_square {
my #arrays = #_;
return [ map {sum #$_} #arrays ];
}
say join ', ' => #{ sum_square([1,2], [4,5]) };
Output:
3, 9
Since this is Perl, it could be expressed in a more compact way.
Shortification
sub sum_square { [ map {sum #$_} #_ ] }
say join ', ' => #{ sum_square([1,2], [4,5]) };
Shortification2
say join ', ' => map {sum #$_} [1,2], [4,5];
Edit: sum the other way round
If the function should be a column sum instead of a line sum, this modification should do the trick (iterate over the indices of the first array):
sub sum_square {
my #arrays = #_;
return [ map { my $i = $_; # $i: all indices of the first array
sum map $_->[$i] => #arrays # sum over all $i-th values of #arrays
} 0 .. $#{$arrays[0]} ];
}
Output:
5, 7