neversaint,
The following code does what you want

#!/usr/bin/perl
use strict;
use warnings;
use Data::Dumper;

my @nar = (
    ['fact 1 - ParamGrp1', 'foo', 'bar'],
    ['fact 1 - ParamGrp2', 'qux', 'bom'],
    ['fact 1 - ParamGrp1', 'fuu', 'gong'],
    ['fact 2 - ParamGrp1', 'fiu', 'ging'],
);
my %data;
for my $elem ( @nar ) {
    my ($key, @val) = @$elem;
    my ($key_1, $key_2) = split " - ", $key;
    push @{ $data{$key_1}{$key_2} }, [ @val ];
}
print Dumper(\%data);
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It has been over 3 weeks since I have written a single line of code so please forgive me for posting a working solution without really answering the question being asked.