yet another observation:
perl arrays and lists are different in the sense that enclosing a ( ) around a bunch of numbers will concatenate them when used under a comma operator, while
when used under a [ ] they retain their identity.
my @data = ( @xvalues, @yvalues )
concatenates xvalues and yvalues. if xvalues/yvalues is an array then they get concatenated.
however if they are lists [ ], they retain their identity.