Oh! You keep talking about avoiding duplicates in a hash, but your problem is actually with avoiding duplicates in an array.

A common idiom to weed out duplicates is: (from perlfaq4) 

my %seen;
my @array = grep !$seen{$_}++, LIST;

[download]

To insert at the same time, that would be 

my %seen;
my @array = grep !$seen{$_}++, @array, $new_value;

[download]

Plug it in and get: 

my %edges;
while (<STREAM>) {
   my($node1, $node2) = split;
   my %seen;
   @{$edges{$node1}} = grep !$seen{$_}++, @{$edges{$node1}}, $node2;
}

[download]

A faster (but more memory hungry) version would be: 

my %edges;
my %seen;
while (<STREAM>) {
   my($node1, $node2) = split;
   next if !$seen{$node1}{$node2}++;
   push @{$edges{$node1}}, $node2;
}

[download]

In reply to Re^5: Tie::Hash::MultiValue Unique question by ikegami
in thread Tie::Hash::MultiValue Unique question by elsubliminal

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