Create a second hash, with countries as the keys; the hash value for each country will be an anonymous array containing the cities belonging to that country:

#! perl
use strict;
use warnings;

my %h1 = 
(
    'Chicago, USA'       => undef,
    'Frankfurt, Germany' => undef,
    'Berlin, Germany'    => undef,
    'Washington, USA'    => undef,
    'Helsinki, Finland'  => undef,
    'New York, USA'      => undef,
);

my %h2;

for (keys %h1)
{
    my  ($city, $country) = split ', ';
    push @{ $h2{$country} }, $city;
}

for (sort keys %h2)
{
    print "$_: ", join(', ',  sort { $a cmp $b } @{ $h2{$_} }), "\n";
}

[download]

Output:

16:29 >perl 819_SoPW.pl
Finland: Helsinki
Germany: Berlin, Frankfurt
USA: Chicago, New York, Washington

16:31 >

[download]

Note: Perl autovivifies the new $h2{$country} elements as needed.

Hope that helps,

Athanasius <°(((>< contra mundum Iustus alius egestas vitae, eros Piratica,

In reply to Re: Hash in Perl by Athanasius
in thread Hash in Perl by rammohan

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