I was playing with this code which swaps hash values: 
use strict;

my %hash = (
  1 => 'angel',
  2 => 'buffy',
  3 => 'cordelia',
  4 => 'dawn',
  5 => 'ethan',
  6 => 'faith',
  7 => 'giles'
);

reorder(5,'up'); # ethan moves up: swaps place with dawn

display();

sub reorder(){
  my ($item,$direction) = @_;
  if($direction eq 'up'){   # coming soon -- 'down'
    my $tmp = $hash{$item}; # save ethan
    $hash{$item} = $hash{ ($item -1) }; # move dawn down to 5
    $hash{ ($item -1) } = $tmp; # put ethan back as 4
  }
}


sub display {
    print '-' x 30,"\n";
  foreach my $key (sort (keys (%hash))) {
    printf("%12s is now number %d\n",$hash{$key},$key);
  }
    print '-' x 30,"\n";
}

[download]

Which works just fine, but then I thought, I wonder if perl can just swap the values for me and changed the reorder sub to this: 

sub reorder(){
  my ($item,$direction) = @_;
  if($direction eq 'up'){
    $hash{$item,($item -1)} = $hash{ ($item -1), $item};
    # maybe perl can automagically do the $tmp thing for me?
  }
}

[download]

but when I ran it that way, I got this output: 

------------------------------
       angel is now number 1
       buffy is now number 2
    cordelia is now number 3
        dawn is now number 4
       ethan is now number 5
             is now number 5
       faith is now number 6
       giles is now number 7
------------------------------

[download]

Which doesn't make sense to me. I now have two number fives in my hash? That's not possible!

I know there's something fundamentally illogical about trying to order hashes when I could be using arrays, but leaving that aside, what happened here?
--

“Every bit of code is either naturally related to the problem at hand, or else it's an accidental side effect of the fact that you happened to solve the problem using a digital computer.”
M-J D

In reply to Swapping Two Hash Values by Cody Pendant

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