### Re^2: Maximum length of hash key ?

 on Aug 19, 2012 at 16:37 UTC ( #988338=note: print w/replies, xml ) Need Help??

in reply to Re: Maximum length of hash key ?
in thread Maximum length of hash key ?

My problem was to merge same hash values when their keys must be combined too.
For ex. %h=( a=>123, b=>123, c=>12);
the output will be :
%h =( "a;b"=>123 ,c=>12);
But because I wasn't sure about the allowed size of the key , I have used md5 hashes for keys. After that I used a temp hash of arrays to store different keys .
But nice to know that it's not limited , makes life much easier ;)

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Re^3: Maximum length of hash key ?
by Marshall (Abbot) on Aug 20, 2012 at 08:11 UTC
Is this going in the right direction for you?
Sounds like you just need a HoA (Hash of Array).
```#!/usr/bin/perl -w
use strict;
use Data::Dump qw(pp);

my %h=( a=>123, b=>123, c=>12);

print pp \%h; #{ a => 123, b => 123, c => 12 }
print "\n";

# Access each key's value in the %h hash...
#
# Each "new key" in the reversed hash is a
# unique value from the %h hash, i.e., \$hash{\$key}
#
# But each one of these new "keys" can contain
# multiple values, so that means that the
# reversed hash has to be a more complex data
# structure, a hash of pointers to array...
#
# Each one of the keys of the "reversed hash" is
# a value from the original hash. They now become keys
# of that "reversed hash" and they have as a value,
# a reference to an array of the keys of the original hash.

my %reversed;
foreach my \$key (keys %h)
{
# the value of \$h{\$key} is the new key
# could have been:
#    my \$new_key = \$h{\$key};
#    push @{\$reversed{\$new_key}}, \$key;
# but this is the same...

push @{\$reversed{\$h{\$key}}}, \$key;
}

print pp \%reversed; #{ 12 => ["c"], 123 => ["a", "b"] }
print "\n";

__END__
{ a => 123, b => 123, c => 12 }
{ 12 => ["c"], 123 => ["a", "b"] }
Update: We are very far from needing MD5 keys. I am responding to your clarification of what you want for the output. Please respond to my post with other details if I didn't get it right...And I don't see that this has to do with maximum key length (which is pretty much unlimited).
Re^3: Maximum length of hash key ?
by Anonymous Monk on Aug 19, 2012 at 21:51 UTC
For ex. %h=( a=>123, b=>123, c=>12); the output will be : %h =( "a;b"=>123 ,c=>12);
... sounds like an inverted list, to me.
```%h = { "123" => [ "a", "b" ], "12" => [ "c" ] };

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