Hi, It's been 11 years since first proposed, but here it is at last. I'm releasing a prereview of ranked indices for Boost.MultiIndex: struct person { int age; std::string name; }; typedef multi_index_container< person, indexed_by< ranked_non_unique >, ordered_non_unique>>> multi_t; multi_t m={{40,"Joe"},{25,"Jill"},{30,"Kurt"},{32,"Sue"}}; auto it=m.emplace(31,"Maggie").first; std::cout<age<<" years old\n"; Ranked indices add a bunch of extra rank-related capabilities to the interface of ordered indices. The rank of an element is its numerical position in the index. nth(i) returns an iterator to the element with rank i, whereas rank(it) is the inverse operation. Both execute in log(n) time. Additionally, the member functions find_rank lower_bound_rank upper_bound_rank equal_range_rank range_rank behave as their "_rank"-less counterparts except they return ranks rather than iterators. One drawback of ranked indices wrt ordered indices (other than their slower perfomance and higher memory consumption) is that deletion of elements is log(n) (in ordered indices it is constant time). Download lib preview: http://tinyurl.com/kemwk8q Tutorial: http://tinyurl.com/q36c9f7 Reference: http://tinyurl.com/pvoulgr For people interested in this, I'd appreciate if you could download the source, copy it on top of Boost 1.58 (1.57 should work as well), play a bit with the new feature and report your results. Also, opinions on naming are welcome. Target version for releasing is Boost 1.59, so we have plenty of time to discuss the design before it is final. Thank you, Joaquín M López Muñoz Telefónica