Re: [Boost-users] [multi_index] Sorting object based on some specified criteria !!

From: Joaquin M Lopez Munoz (joaquin_at_[hidden])
Date: 2006-04-17 15:26:14

Patel Priyank-PPATEL1 <priyankpatel <at> motorola.com> writes:

> 
> 
> Hi 
> all,
> 
> Â 
> I have following 
> kind of class and having some identifier and group id associated 
> with
> particular 
> procedure. I want to know if I have to get the procedures relating particular 
> 
> group for ex. 
> (groupId == 1). How do I do using multiindex container? Can 
> somebody
> please give me some 
> hint or code if they have done something similar to what I 
> want
> to do? 
>

Hello Priyank, I'm not sure I've understood what you're after,
but let me try anyway:

As you'll search for group, you'll need an additional index
(the one you've set up is based on process ID). The following
has not been compiled, beware typos:

  struct id {};
  struct group {};
  
  typedef 
  multi_index_container<
    Procedure*,
    indexed_by<
      hashed_unique<
       tag<id>, 
       const_mem_fun<Procedure, int, &Procedure::get_id> >
      >,
      hashed_non_unique<
       tag<group>, 
       const_mem_fun<Procedure, int, &Procedure::get_group> >
      >
    >
  >
  Procedure_Hashed_Pool;
  
  typedef Procedure_Hashed_Pool::
    index<id>::type               Procedure_By_Id; 
  typedef Procedure_Hashed_Pool::
    index<group>::type            Procedure_By_Group; 

(I've decided to make the new index hashed non-unique,
you could also have it ordered non-unique if you need
the elements to be sorted by group ID --hashing only
guarantees fast retrieval.)
And now you can simply use equal_range() on this index
to do what you want:

  int gr=...;
  const Procedure_By_Group& procedure_bg=
    procedure_pool.get<group>();
  std::pair<
    Procedure_By_Group::iterator,
    Procedure_By_Group::iterator
  > p=procedure_bg.equal_range(gr);

p will hold the range of elements with group ID == gr.

Is this what you were after?

Joaquín M López Muñoz
Telefónica, Investigación y Desarrollo