Re: [Boost-users] Multi Index: Nested std::pair

Etienne Philip Pretorius escribió:

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Hi Etienne,

Could you please elaborate on what is meant by "unique values"? This is not clear to me from the explanations on your previous posts. It might help to state your requirements in the reverse way: what kind of duplications involving value should be banned from the container? For instance, the ordered_unique index you show us above bans duplicate elements having the same form (x,*,value), where * indicates that the y member is immaterial here.

Hello Joaquín,

I am doing a matrix operation where I need to know the number of unique values per x co-ordinate and number of unique values per y co-ordinate.

N-th row, x=N, but how many unique "values" are there in this row? N-th column, y=N, but how many unique "values" are there in the column?

Hi Etienne, I'm not compleetely sure I'm getting you, but let me try. If by unique values you simply mean all the elements with given x coordinate, you can write: std::size_t values_with_x(const matrix_t& m,unsigned char x) { return m.get<1>().count(x); } However, if you're after elements with a given x coordinate having *distinct* values, you can define your container as typedef boost::multi_index_container< element_t, boost::multi_index::indexed_by< /*value*/ boost::multi_index::ordered_non_unique< boost::multi_index::member< element_t, unsigned char, &element_t::value > >, /*x co-ordinate*/ boost::multi_index::ordered_non_unique< boost::multi_index::composite_key< element_t, boost::multi_index::member< element_t, unsigned char, &element_t::x >, boost::multi_index::member< element_t, unsigned char, &element_t::value > > >, /*y co-ordinate*/ boost::multi_index::ordered_non_unique< boost::multi_index::composite_key< element_t, boost::multi_index::member< element_t, unsigned char, &element_t::y >, boost::multi_index::member< element_t, unsigned char, &element_t::value > > > >

matrix_t;

and write the following: std::size_t distinct_values_with_x(const matrix_t& m,unsigned char x) { typedef matrix_t::nth_index<1>::type index_t; typedef index_t::iterator iterator; std::pair p=m.get<1>().equal_range(x); std::size_t res=0; while(p.first!=p.second){ ++res; p.first=m.get<1>(). upper_bound(boost::make_tuple(p.first->x,p.first->value)); } return res; } Does this approach your goal? Please find attached a complete test program. Joaquín M López Muñoz Telefónica, Investigación y Desarrollo #include #include #include #include #include <iostream> struct element_t { element_t( unsigned char value, unsigned char x, unsigned char y ):value(value),x(x),y(y){} unsigned char value; unsigned char x; unsigned char y; }; typedef boost::multi_index_container< element_t, boost::multi_index::indexed_by< /*value*/ boost::multi_index::ordered_non_unique< boost::multi_index::member< element_t, unsigned char, &element_t::value > >, /*x co-ordinate*/ boost::multi_index::ordered_non_unique< boost::multi_index::composite_key< element_t, boost::multi_index::member< element_t, unsigned char, &element_t::x >, boost::multi_index::member< element_t, unsigned char, &element_t::value > > >, /*y co-ordinate*/ boost::multi_index::ordered_non_unique< boost::multi_index::composite_key< element_t, boost::multi_index::member< element_t, unsigned char, &element_t::y >, boost::multi_index::member< element_t, unsigned char, &element_t::value > > > >

matrix_t;

std::size_t values_with_x(const matrix_t& m,unsigned char x) { return m.get<1>().count(x); } std::size_t distinct_values_with_x(const matrix_t& m,unsigned char x) { typedef matrix_t::nth_index<1>::type index_t; typedef index_t::iterator iterator; std::pair p=m.get<1>().equal_range(x); std::size_t res=0; while(p.first!=p.second){ ++res; p.first=m.get<1>(). upper_bound(boost::make_tuple(p.first->x,p.first->value)); } return res; } int main() { matrix_t m; m.insert(element_t(0,0,0)); m.insert(element_t(0,0,0)); m.insert(element_t(1,0,0)); m.insert(element_t(1,0,0)); m.insert(element_t(2,0,0)); m.insert(element_t(4,0,0)); std::cout<