[boost] [multi_index] container for groups?

From: Janek Kozicki (janek_listy_at_[hidden])
Date: 2007-07-17 09:45:06

Hello,

I just wanted to check grounds before I get to implementing this
(don't know when ;). I want a container that allows to assign several
groups (sth. like std::set<int> ) to id numbers (int). Let's say that I
have following id numbers: 1,3,5,7. And I assign that 1 belongs to
groups 1,2,3. Then I say that 2 belongs to groups 2,3,4. And 5
belongs to groups 2,4 and finaly 7 belongs to groups 1,4. So it would look like:

id: groups
1 : 1,2,3
3 : 2,3,4
5 : 2,4
7 : 1,4

Using this container I want to iterate in all possible ways:

- iterate over all ids from start to end - answer: 1,3,5,7
- iterate over all ids which belong to group 3 - answer: 1,3
- iterate over all groups from start to end - answer: 1,2,3,4
- iterate over all groups in which id 5 appears - answer: 2,4

I guess that this should be easy with multi_index, since that's what
for they were designed :-)

Also it would be nice to be able to give names to *some* groups. I
expect to have about 10000 groups in a program (iterating over all id
numbers from group 787 must be really quick!), and the user might
want to name few groups. This can be slow, since it's only for GUI
and user interaction. But I don't want to store a string with each
group even if it's empty. With 10000 groups that would waste too much
memory. I prefer to only store strings for groups which indeed have names,
like that:

group 1 : Walls
group 2 : Grains

other groups unnamed.

can you give me some hints about how to approach that?
-- 
Janek Kozicki                                                         |