my %seen;
my $num_unique_users =
    grep !$seen{ $HoH{$_}{user} }++,
    keys(%HOH);

[download]

If you actually want the name of the users: 

my %seen;
my @unique_users =
    grep !$seen{ $HoH{$_}{user} }++,
    keys(%HOH);

[download]
my %seen;
my @unique_users =
    grep !$seen{$_}++,
    map $HoH{$_}{user},
    keys(%HOH);

[download]

In reply to Re: Retrieve unique values from Hash of Hashes by ikegami
in thread Retrieve unique values from Hash of Hashes by snra_perl

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