my $hash;
foreach my $csn (keys %$datastore) {
  push @{$hash->{$datastore->{$csn}->[3]}}, $datastore->{$csn}->[0];
}

foreach  (keys %$hash) {
    my @sorted = sort { $a <=> $b } @{$hash->{$_}};
    $hash->{$_} = \@sorted;
}

foreach  (keys %$datastore) {
	$datastore->{$_} = [$datastore->{$_}->[1],$datastore->{$_}->[2],$datastore->{$_}->[3], indexof($hash->{$datastore->{$_}->[3]}, $datastore->{$_}->[0])];
}


sub indexof{
	my ($array_ref, $search_for)  = (shift, shift);
	my @array = @$array_ref;
	my( $index )= grep { $array[$_] eq $search_for } 0..$#array;
	return ($index + 1);
}