use Data::Dumper;

%x =
  ( 3 => 4,
    1 => 5
  );

print Dumper(\%x), $/;

%x =
  (  1 => 2,
     3 => $x{1}
  );


print Dumper(\%x), $/;

##</code><code>##

$VAR1 = {
          1 => 5,
          3 => 4
        };

$VAR1 = {
          1 => 2,
          3 => 5
        };