my @return = correlation(\@primarys_array, \@secondarys_array);
use Data::Dumper;  warn Dumper \@return;

##</code><code>##

# note -- it's a scalar ($) not a hash (%)
my $hashref_return_A =  correlation(\@primarys_array, \@secondarys_array);

# or 
# %{ ... } casts a hashref to a list
my (%hashref_return_A) = %{ correlation(\@primarys_array, \@secondarys_array) };