I would use a hash reference. See perldata and perlref. Are you still struggling with LineFit.pm error due to undef value?

use strict;
use warnings;
use Statistics::LineFit;
use Data::Dumper;

sub get_hashref {
    my ($x_ref, $y_ref) = ([1,2,3], [4,5,6]);
    my $lfit = Statistics::LineFit->new();
    $lfit->setData($x_ref, $y_ref);

    my ($intercept, $slope) = $lfit->coefficients();
    my $rSquared = $lfit->rSquared();

    my $hashref = {
      a => $intercept, 
      b => $slope, 
      c => $rSquared
    };

    return $hashref;
}

# ------ main ------
my $hr = get_hashref();
print Dumper($hr);

__END__

$ perl -l 652420.pl
$VAR1 = {
          'c' => '1',
          'a' => '3',
          'b' => 1
        };
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