Another idea for you... Sometimes Hash of Array is useful. 
#!/usr/bin/perl
use strict;
use warnings;

my %hash;

while (my $line = <DATA>)
{
    next if $line =~ /^\s*$/; #skip blanks
    chomp $line;

    my ($value, $key) = split ':',$line,2;
    push @{$hash{$key}},$value;
}

foreach my $key (sort keys %hash)
{
    print "$key => @{$hash{$key}} ERROR Single Node!\n" if @{$hash{$ke
+y}}<2;
}

=prints
vg3:38 => node1 ERROR Single Node!
vg3:40 => node2 ERROR Single Node!
=cut

__DATA__
node1:vg1:36
node2:vg1:36
node1:vg2:37
node2:vg2:37
node1:vg3:38
node2:vg3:40

[download]
Update: I did a very poor job of naming in the above example. Normally I would call a hash by the names of the values it contains...instead of just %hash, %nodes would be better. Of course some descriptive name for "vg1:36" is far better that just "$key". With the good names, foreach my $machine_port (sort keys %nodes) is much more readable. I have no idea whether "machine_port" is right or not because I have no idea what "vg1:36" means in the real world.

HoA can be useful because multidimensional hashes require a loop for each dimension in order to traverse the entire HoHoH..

In reply to Re: Compare the values in the hash by Marshall
in thread Compare the values in the hash by perl_5eeker

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