Here's a working solution that, I believe, does all the things you want.

#!/usr/bin/env perl

use strict;
use warnings;

my $wanted_type = q{hyper};
my %data_capture = ();

while (<DATA>) {
    my @fields = split;

    if ($fields[2] eq $wanted_type) {
        push @{$data_capture{$fields[0]}}, $fields[3];
    }
}

for my $key (keys %data_capture) {
    print $key, q{-->(}, join(q{, }, @{$data_capture{$key}}), qq{)\n};
}

__DATA__
alligator-n    amphibian_reptile    event    sleep-v
alligator-n    amphibian_reptile    event    swim-v
alligator-n    amphibian_reptile    event    walk-v
alligator-n    amphibian_reptile    hyper    animal-n
alligator-n    amphibian_reptile    hyper    beast-n
alligator-n    amphibian_reptile    hyper    carnivore-n
alligator-n    amphibian_reptile    mero     foot-n
alligator-n    amphibian_reptile    mero     jaw-n
[download]

This code outputs:

$ pm_array_of_arrays.pl
alligator-n-->(animal-n, beast-n, carnivore-n)
[download]

Update: I simplified the if statement because autovivification handles what I (superfluously) coded. It use to look like this:

    if ($fields[2] eq $wanted_type) {
        if (! exists $data_capture{$fields[0]}) {
            $data_capture{$fields[0]} = [];
        }
        push @{$data_capture{$fields[0]}}, $fields[3];
    }
[download]

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