The simplest way I know to swap values for hash keys is with a slice: @hash{ 'foo', 'bar' } = @hash{ 'bar', 'foo'};

After Compline,
Zaxo

The simplest way I know to swap values for hash keys is with a slice:

That's what he tried to do. He just got the syntax wrong.

Cody, instead of

$hash{$item,($item -1)} = $hash{ ($item -1), $item};
[download]

try

@hash{$item, ($item - 1)} = @hash{($item - 1), $item};
[download]

Pay careful attention to the sigils. You have to use an @ to specify a slice.

-sauoq
"My two cents aren't worth a dime.";

If your keys are always numeric, the you shoudln't be using a hash. That's what arrays are for...:)

Notice thta this way, your don't need to sort in display().

use strict;

my @array = (
'angel',
'buffy',
'cordelia',
'dawn',
'ethan',
'faith',
'giles',
);


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

display();

sub reorder {
    my ($item,$direction) = @_;

      ### Adjust index as arrays start at 0
    $item--; 

      # Down is here :) - you should add bounds checking!
    my $other = $direction eq 'up' 
                ? $item - 1 
                : $item + 1;
    @array[$item, $other] = @array[$other, $item];
    return;
}


sub display {
  print '-' x 30,"\n";
 foreach my $key (0..$#array) {
  printf("%12s is now number %d\n",$array[$key],$key+1); ##Adjust key 
+for display.
 }
  print '-' x 30,"\n";
}
__END__
D:\Perl\test>test
------------------------------
       angel is now number 1
       buffy is now number 2
    cordelia is now number 3
       ethan is now number 4
        dawn is now number 5
       faith is now number 6
       giles is now number 7
------------------------------
[download]

I think someone has to ask: why aren't you using an array for this? You are basically implementing an array on top of a hash anyway by using the hash keys as indexes.

-sauoq
"My two cents aren't worth a dime.";

I'm not using an array because I'm not very smart, but thanks for pointing it out.

I was just pondering data structures, really. If I had some much more complex structure, possibly read out of XML in such a way that it just had to be a hash, I might have wanted to deal with

%hash{
  array => [foo,bar,baz],
  bunchofotherstuff => [array
    [hash{
       array[
         ]
      }
   ],
  order => 1
}
[download]

But don't I get a point for knowing it was stupid? More importantly, I've grasped something about playing with hash values, and I've proved that my instincts about perl having a smart way to do stuff like that were right.
--


“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

sub reorder {
  my ($item,$direction) = @_;
  if($direction eq 'up'){
    @hash{$item,$item-1} = @hash{$item-1,$item};
  }
}
[download]

-enlil

@hash{$item,$item-1} = @hash{$item-1,$item};
[download]

Aha! Now I see what I was doing wrong -- I had

$hash{$item,$item-1} = $hash{$item-1,$item};

So I probably created another key which is not 5 but 5-undef or something?

Thank you both very much.
--


“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

Yup, you're correct, you can't have duplicate keys.. and you haven't.. try this..

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";

  foreach my $key (sort keys %hash) {
    print "$key = $hash{$key}\n";
  }

  print '-' x 30,"\n";
}
__END__

prints:
------------------------------
       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
------------------------------
1 = angel
2 = buffy
3 = cordelia
4 = dawn
5 = ethan
54 =
6 = faith
7 = giles
------------------------------
[download]

cheers,

J

Hashes can have duplicate VALUES, but not duplicate KEYS. You assigned a value to the key of '', probably because your assignment statement's left side's key expression evaluated to undef. (Undef stringizes as ''.)

I shouldn't scan so quickly, the odd values-first printout threw me off. However, this should explain your odd "duplicate keys" mystery.

%hash = (
          '1' => 'angel',
          '2' => 'buffy',
          '3' => 'cordelia',
          '4' => 'dawn',
          '5' => 'ethan'
          '54' => undef,
          '6' => 'faith',
          '7' => 'giles',
        );
[download]

The printf "%d" turned the key '5 4' into an integer '5'.

--
[ e d @ h a l l e y . c c ]

You assigned a value to the key of ''
[download]

Huh? I'm really confused now. The key is the number, not the name. That display says the value is undef and the key is 5.
--


“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

Ed got this one wrong, Cody. Listen to Zaxo.

-sauoq
"My two cents aren't worth a dime.";

Makeshifts last the longest.