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

From: Patel Priyank-PPATEL1 (priyankpatel_at_[hidden])
Date: 2006-04-17 15:36:25

Hi Joaquin,

First of all thanks for your time and response. I have it working as follows, but seems I have to recalculate iterators if in case I later on modify group associated with that access point. Is there any way that iterators will know automatically update when I update access point in future to some other group? 
Let me know if you have come across that one. I am going to look in your code in detail and get back to you in case of any questions.

Thanks
Priyank

// class Access point test
class Access_Point {
public:
        Access_Point(int id, int paging_group):id_(id), pg_(paging_group) {
        }
        bool by_id(int _id) const {
                return (_id == id_);
        }
        int paging_group(int _pg) const {
                return (_pg == pg_);
        }
        int id() const {
                return id_;
        }
        int pg() const {
                return pg_;
        }
        int pg(int _pg) {
                pg_ = _pg;
        }
        friend ostream& operator << (ostream& _os, const Access_Point& _ap);
private:
        int id_;
        int pg_;
};
ostream& operator << (ostream& _os, const Access_Point& _ap)
{
        _os << "Id: " << _ap.id_ << "Pg: " << _ap.pg_ << endl;
        return _os;
}

// tag ids
struct hashed_objs {
};
struct paging_group {
};

// Create multi index container

typedef multi_index_container<
Access_Point*,
indexed_by<

hashed_unique<
tag<hashed_objs>, const_mem_fun<Access_Point, int, &Access_Point::id> >,

ordered_non_unique <
tag<paging_group>, const_mem_fun<Access_Point, int, &Access_Point::pg>
>

>
> Access_Points;
 
int ACE_MAIN (int, ACE_TCHAR *[])
{ 
// ACCESS POINT CHECK
        Access_Points pool;
        Access_Point * a1 = new Access_Point(1, 1);
        Access_Point * a2 = new Access_Point(2, 1);
        Access_Point * a3 = new Access_Point(3, 2);
        Access_Point * a4 = new Access_Point(4, 1);
        // insert all the access points
        pool.insert(a1);
        pool.insert(a2);
        pool.insert(a3);
        // get iterator
        index_iterator<Access_Points, paging_group>::type pg0, pg1;
        boost::tuples::tie(pg0, pg1) = get<paging_group> (pool).equal_range(1);
        pool.insert(a4);
        // print all that is there
        while (pg0 != pg1) {
                cout << *(*pg0) << endl;
                pg0++;
        }

        // change paging group from access point 4
        a4->pg(2);
        // NEED TO RECALCULATE ITERATORS
        boost::tuples::tie(pg0, pg1) = get<paging_group> (pool).equal_range(1);
        while (pg0 != pg1) {
                cout << *(*pg0) << endl;
                pg0++;
        } 
        // return success
        return 0;
}

-----Original Message-----
From: boost-users-bounces_at_[hidden] [mailto:boost-users-bounces_at_[hidden]] On Behalf Of Joaquin M Lopez Munoz
Sent: Monday, April 17, 2006 2:26 PM
To: boost-users_at_[hidden]
Subject: Re: [Boost-users][multi_index] Sorting object based on some specified criteria !!

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

> 
> 
> Hi
> all,
> 
>  
> 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

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