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get the rank of an element of a boost::multi_index container


get the rank of an element of a boost::multi_index container

By : Xiao.Zhou
Date : November 22 2020, 09:00 AM
will be helpful for those in need @sehe's answer is perfectly valid but runs in linear time. If you want better performance, consider defining your index #0 as random_access and #1 as ranked_non_unique (index #2 is redundant):
code :
typedef multi_index_container <
    int
  , indexed_by<
        random_access<>
      , ranked_non_unique<identity<int>>
    >
> Ints;
std::cout
    << "rank of next by sequence is "
    << ints.project<0>(it)-sequence.begin()+1 // O(1)
    << std::endl
;
std::cout
    << "rank of next by order is "
    << order.rank(it)+1 // O(log n)
    << std::endl
;


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Boost multi_index container with composite key, custom comparer and partial index search

Boost multi_index container with composite key, custom comparer and partial index search


By : Daniele Acquaroli
Date : March 29 2020, 07:55 AM
searching a boost multi_index container the fastest possible way

searching a boost multi_index container the fastest possible way


By : user4588053
Date : March 29 2020, 07:55 AM
it helps some times I don't quite get the overall subsequence matching strategy you follow, but focusing on the code alone there are two things you can do to improve efficiency:
code :
std::distance(get<1>(data).begin(),next)
typedef multi_index_container <
    float
  , indexed_by <
        ordered_non_unique<identity<float>>
      , random_access<>
    >
> Floats;
lower=data.get<0>().lower_bound(*i-0.001);
upper=data.get<0>().lower_bound(*i+0.001);
std::tie(lower,upper)=data.get<0>().range(
    [lo=*i-0.001](float x){return lo<=x;},
    [hi=*i+0.001](float x){return x<=hi;}
);
how to get an intersection of a boost::multi_index container

how to get an intersection of a boost::multi_index container


By : Mueed Chaudhry
Date : March 29 2020, 07:55 AM
fixed the issue. Will look into that further OK, now I understand you'd like to search 4-dimensional points in the region [x0,x0+d]×[x1,x1+d]×[y0,y0+d]×[y1,y1+d], right?
Well, I'm afraid to say Boost.MultiIndex is not the right tool for that, as obtaining the intersection of ranges in indices #0, #1, #2, #3 can only be done by scanning one of the ranges (say #0) and manually verifying if the traversed points' remaining coordinates (x1, y0, y1) lie within the area of interest (std::set_intersection does not even apply here as it requires that compared ranges be sorted by the same criterion, which is not the case for our indices).
How to iterate through the indices of a Boost Multi_index container?

How to iterate through the indices of a Boost Multi_index container?


By : Junfeng Gao
Date : March 29 2020, 07:55 AM
should help you out If you can't use C++14, the backporting to C++03 with Boost could look like this:
Live Coliru Demo
code :
#include <boost/type_traits/integral_constant.hpp>

template<typename T,T N0,T N1,typename F>
void static_for(F f)
{
  static_for<T,N0,N1>(f,boost::integral_constant<bool,(N0<N1)>());
}

template<typename T,T N0,T N1,typename F>
void static_for(F f,boost::true_type)
{
  f(boost::integral_constant<T,N0>());
  static_for<T,N0+1,N1>(f);
}

template<typename T,T N0,T N1,typename F>
void static_for(F f,boost::false_type)
{
}

#include <boost/multi_index_container.hpp>
#include <boost/multi_index/ordered_index.hpp>
#include <boost/multi_index/identity.hpp>

using namespace boost::multi_index;
typedef multi_index_container<
  int,
  indexed_by<
    ordered_non_unique<identity<int> >,
    ordered_non_unique<identity<int>,std::greater<int> >,
    ordered_non_unique<identity<int> >,
    ordered_non_unique<identity<int>,std::greater<int> >,
    ordered_non_unique<identity<int> >,
    ordered_non_unique<identity<int>,std::greater<int> >
  >
> result_multi;

#include <iostream>

struct body
{
  body(result_multi& result):result(result){}

  template<typename I>
  void operator()(I){
    typename result_multi::nth_index<I::value>::type& index=
      result.get<I::value>();

    std::cout<<"index #"<<I::value<<": ";
    for(typename result_multi::nth_index<I::value>::type::iterator
          b=index.begin(),
          e=index.end();
        b!=e;++b){
      std::cout<<*b<<" ";
    }
    std::cout<<"\n";
  }

  result_multi& result;
};

int main()
{
  result_multi result;
  for(int i=0;i<3;++i)result.insert(i);

  static_for<int,0,6>(body(result));
}
#include <boost/multi_index_container.hpp>
#include <boost/multi_index/ordered_index.hpp>
#include <boost/multi_index/identity.hpp>

using namespace boost::multi_index;
typedef multi_index_container<
  int,
  indexed_by<
    ordered_non_unique<identity<int> >,
    ordered_non_unique<identity<int>,std::greater<int> >,
    ordered_non_unique<identity<int> >,
    ordered_non_unique<identity<int>,std::greater<int> >,
    ordered_non_unique<identity<int> >,
    ordered_non_unique<identity<int>,std::greater<int> >
  >
> result_multi;

#include <boost/preprocessor/repetition/repeat.hpp>
#include <iostream>

int main()
{
  result_multi result;
  for(int i=0;i<3;++i)result.insert(i);

#define BODY(z,i,_)                                        \
{                                                          \
  result_multi::nth_index<i>::type& index=result.get<i>(); \
                                                           \
  std::cout<<"index #"<<i<<": ";                           \
  for(result_multi::nth_index<i>::type::iterator           \
        b=index.begin(),                                   \
        e=index.end();                                     \
      b!=e;++b){                                           \
    std::cout<<*b<<" ";                                    \
  }                                                        \
  std::cout<<"\n";                                         \
}

BOOST_PP_REPEAT(6,BODY,~)

#undef BODY
}
Explicit instantion of boost multi_index container

Explicit instantion of boost multi_index container


By : yunchen
Date : March 29 2020, 07:55 AM
around this issue If the type is part of a class' visible interface then any headers that class is dependent on have to be included, no way around that. If you really don't want it to be part of the visible interface consider using the pImpl idiom:
Public header
code :
#if !defined(MYCLASS_PUBLIC_H_)
#define MYCLASS_PUBLIC_H_

struct MyClassImpl;
class MyClass {
  MyClassImpl * pImpl;
public:
  void SomeOperation();
};
#endif
#if !defined(MYCLASS_IMPL_H_)
#define MYCLASS_IMPL_H_
#include <private_type.h>
#include "MyClass.h"
struct MyClassImpl
{
  void Operation();

private:
  SomePrivateType member;
};
#endif
#include "MyClassImpl.h"
void MyClass::SomeOperation()
{
  pImpl->Operation();
}

void MyClassImpl::Operation()
{
  // do something with 'member'
}
#include "MyClass.h"
void foo()
{
  MyClass inst;
  inst.SomeOperation();
}
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