Hash key ordering question

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
}
[download]

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
[download]

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

Comment on Hash key ordering question Select or Download Code

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${.02}`	[reply]
Re: Re: Hash key ordering question by P0w3rK!d (Pilgrim) on May 07, 2003 at 18:17 UTC
Thank you :)	[reply]
Re: Hash key ordering question by artist (Parson) on May 07, 2003 at 18:20 UTC
Look at Re: Printing a hash in a specific order? for an example of Tie::IxHash. artist	[reply]
Re: Hash key ordering question by jkenneth (Pilgrim) on May 07, 2003 at 18:52 UTC
Ummm, the numbers are sequential, so why not use an array? `for ($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]
Re: Re: Hash key ordering question by hardburn (Abbot) on May 07, 2003 at 19:22 UTC
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	[reply]
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]
Re: Re: Hash key ordering question by shemp (Deacon) on May 07, 2003 at 18:43 UTC
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]
Re: Re: Re: Hash key ordering question by P0w3rK!d (Pilgrim) on May 07, 2003 at 19:18 UTC
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]
Re: Re: Re: Hash key ordering question by jgallagher (Pilgrim) on May 07, 2003 at 21:55 UTC
Thanks. That completely slipped my mind.	[reply]


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