P0w3rK!d has asked for the wisdom of the Perl Monks concerning the following question:

Hi, I built a HoH as follows: 
# build hash
while() {
...
$hshFoo{$key1}{$key2} = $strFileName;
...
# key1 is a number
# key2 is a sequential number
}

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The entries are placed in seqential order such as: 
$hshFoo{2823}{0} = 2823_0.xml
$hshFoo{2823}{1} = 2823_1.xml
$hshFoo{2823}{2} = 2823_2.xml
$hshFoo{2823}{3} = 2823_3.xml

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When I dump the hash, the keys come out as follows: 
    foreach $key1 (keys %hshFoo) {
        foreach $key2 (keys %{$hshFoo{$key1}}) {
            print "$key1/$key2 => $hshFoo{$key1}{$key2}\n";
        }
    }

...
Output:
2823/1 => 2823_1.xml
2823/0 => 2823_0.xml
2823/3 => 2823_3.xml
2823/2 => 2823_2.xml
...
I expected:
2823/0 => 2823_0.xml
2823/1 => 2823_1.xml
2823/2 => 2823_2.xml
2823/3 => 2823_3.xml

[download]
The files were originally placed in the hash from a sorted array. Are the keys not in order within the hash or does Perl just grab the keys in any order?
Just curious. :)

-P0w3rK!d

Replies are listed 'Best First'.
Re: Hash key ordering question
by thelenm (Vicar) on May 07, 2003 at 18:13 UTC
    Yep, hash entries are not ordered in a predictable way. You will have to sort the hash keys yourself, or you may want to look into a module like Tie::IxHash, which preserves the insertion order of hash keys.

    -- Mike

    --
    just,my${.02}

[reply]
      Thank you :)
[reply]
Re: Hash key ordering question
by artist (Parson) on May 07, 2003 at 18:20 UTC
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Re: Hash key ordering question
by jkenneth (Pilgrim) on May 07, 2003 at 18:52 UTC
    Ummm, the numbers are sequential, so why not use an array? 
    
for ($i = 0; $i < 10; $i++) {
   $hash{2823}[$i] = "2823_$i.xml";
}
 
foreach $key (keys %hash) {
   foreach $xml (0..$#{$hash{$key}}) {
      print "Key: $key/$xml => " . $hash{$key}[$xml] . "\n";
   }
}


Key: 2823/0 => 2823_0.xml
Key: 2823/1 => 2823_1.xml
Key: 2823/2 => 2823_2.xml
Key: 2823/3 => 2823_3.xml
Key: 2823/4 => 2823_4.xml
Key: 2823/5 => 2823_5.xml
Key: 2823/6 => 2823_6.xml
Key: 2823/7 => 2823_7.xml
Key: 2823/8 => 2823_8.xml
Key: 2823/9 => 2823_9.xml

    [download]
    JK
[reply]
[d/l]

      I would guess the datastructure is part of a larger program where an array doesn't make sense.

      ----
      I wanted to explore how Perl's closures can be manipulated, and ended up creating an object system by accident.
      -- Schemer

      Note: All code is untested, unless otherwise stated

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Re: Hash key ordering question
by jgallagher (Pilgrim) on May 07, 2003 at 18:30 UTC
    If you want them in numerical order rather than the order you put them in, you could also do: 
    foreach $key1 (sort keys %hshFoo) {
    foreach $key2 (sort keys %{$hshFoo{$key1}}) {
        print "$key1/$key2 => $hshFoo{$key1}{$key2}\n";
    }
}

    [download]
[reply]
[d/l]
      that will actually sort in string comparison order (the default for sort). for numeric order, you want: 
      ...
foreach $key1 (sort {$a <=> $b} keys %hshFoo) {
...

      [download]
[reply]
[d/l]
        This is what I was looking for. I was trying to do something with Tie::IxHash the last 10 minutes. 
            my $t = Tie::IxHash->new(%hshFoo);
    my @keys = $t->Keys;
    $t->Reorder(@keys);
    $t->SortByKey;
    untie %hshFoo;

...or something

        [download]

        -P0w3rK!d

[reply]
[d/l]
        Thanks. That completely slipped my mind.
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