Hi Ovanes, Ovanes Markarian writes:

Hello *,I currently need to implement the following use case and was wondering if this is possible with multi-index: I have a class, for simplicity all members are public wihtout accessors and mutators:

class entry{ public: field x; field y; field z; };

I need a multi-index index to remember the order in which the elements were inserted and non uniquely index the inserted elements by hash of field x; Now a client could do the following queries:- get all entries in the order they were inserted (this is easy and I know how to do it)- get all entries which satisfy field x parameter in the order they were inserted. I know that I can retrieve the values dependent on hash(x), but these are probably not sorted. I know that I can project iterators, but can I project (range_retireved_via_hashed_X) to (range_retrieved_for_sequence_of_X)May be I miss smth here or should split my data in some other way to satisfy this condition.

As I see it, you've got two options here to get the elements with equal x sorted by inclusion order: 1. Use an ordered index instead of (or additionally to) the hashed index: elements with equal key are guaranteedly inserted in insertion order. 2. Retrieve the range from the hashed index and sort it externally according to the insertion order: here random_access indices (http://tinyurl.com/2dvmul )come handy, as you can compare random access iterators for order precedence. So, instead of a sequenced index you'd have something like: typedef multi_index_container< entry, indexed_by< hashed_non_unique >, random_access<> >

multi_t;

and the range retrieval function could look like this: void range_as_inserted(const multi_t& m,field x) { typedef multi_t::nth_index_iterator<1>::type ra_iterator; typedef std::vector buffer; buffer buf; std::pair p=m.equal_range(x); while(p.first!=p.second)buf.push_back(m.project<1>(p.first++)); std::sort(buf.begin(),buf.end()); for(buffer::iterator it=buf.begin(),it_end=buf.end(); it!=it_end;++it){ std::cout<<**it<<"\n"; } } The idea is: store the hash range as a vector of random access iterators to the elements and then just std::sort it, using the fact that a random_access iterator it0 is less than it1 (in our particular case) if it points to an older element (with respecto to insertion time). I can't attach files from Gmane, so please find the pasted code of a complete snippet showing technique #2 Hope this helps, Joaquín M López Muñoz Telefónica, Investigación y Desarrollo -----------------BEGIN CODE----------------- #include #include #include #include #include #include <algorithm> #include <iostream> #include <vector> using namespace boost::multi_index; typedef int field; struct entry { entry(int x,int y):x(x),y(y){} field x,y; }; std::ostream& operator<<(std::ostream& out,const entry& e) { return out< >, random_access<>

multi_t;

void range_as_inserted(const multi_t& m,field x) { typedef multi_t::nth_index_iterator<1>::type ra_iterator; typedef std::vector buffer; buffer buf; std::pair p=m.equal_range(x); while(p.first!=p.second)buf.push_back(m.project<1>(p.first++)); std::sort(buf.begin(),buf.end()); for(buffer::iterator it=buf.begin(),it_end=buf.end();it!=it_end;++it){ std::cout<<**it<<"\n"; } } int main() { multi_t m; for(int i=0;i<60;++i)m.insert(entry(0,i)); range_as_inserted(m,0); } -----------------END CODE-----------------