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RE: Hash Question

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Balint, Jess
February 1, 2002 11:50
RE: Hash Question
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I think I will go ahead and use something like the multi-dimensional hash
example below. What I need to do is create hashes dynamically based on how
many are needed for this particular instance of the program. Any ideas on
dynamic hash creation multi-dimensionally? Thanks	-jess

-----Original Message-----

On Fri, 2002-02-01 at 12:42, Balint, Jess wrote:
> Since this is a beginners list, I thought I would be allowed to ask this
> question. Can there be multiple values for hash keys, or just one? The
> reason I am asking is that I am working on a statistical program and would
> need to use multiple hashes as values of another hash. If this is
> please let me know. Thank you.
> -Jess

I assume you mean a multi-dimensional hash.  Perl allows infinite
(assuming you have the resources) nesting of data structures.  This is
accomplished by using a reference to the structure to be nested.  So for
a three dimension hash you would first have a hash whose values were
hash references.  Then those hashes would have values that were also
references to hashes.  You could then access the data like this:

print $hash{'key1'}->{'key2'}->{'key3'}, "\n";

but Perl being what it is provides a little syntatic suger and lets you
just write this:

print $hash{'key1'}{'key2'}{'key3'}, "\n";

#!/usr/bin/perl -w

use strict;

my %hash;

while (<>) {
        my ($key1, $key2, $key3, $data) = split;

        $hash{$key1}{$key2}{$key3} = $data if $key1 and $key2 and $key3;

foreach my $key1 (sort keys %hash) {
        foreach my $key2 (sort keys %{$hash{$key1}}) {
                foreach my $key3 (sort keys %{$hash{$key1}{$key2}}) {
                        print "($key1)+($key2)+($key3) returns ",
                                $hash{$key1}{$key2}{$key3}, "\n";

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