if ($sorttype == 2) {
    $subsort = ( sub { $a->{key2} <=> $b->{key2} } );
}
elsif ($sorttype == 3) {
    $subsort = ( sub { $a->{key3} <=> $b->{key3} || $a->{defaultKey} <=> $b->{defaultKey} } );
}
elsif ($sorttype == 4) {
    $subsort = ( sub { $b->{defaultKey} <=> $a->{defaultKey} } );
}
elsif ($sorttype == 5) {
    $subsort = ( sub { $b->{key5} cmp $a->{key5} || $a->{defaultKey} <=> $b->{defaultKey} } );
}

$subsort = ( sub{keyComparison || defaultComparison} );

foreach (sort $subsort @dataArray) {
    my $data = $_;
    ...
}

$subsort = ( sub{keyComparison || defaultComparison} );

# versus

$subsort = sub{keyComparison || defaultComparison};