c++ implementing iterators for custom matrix class

Question

I am currently working on a linear algebra library (custom vector and matrix plus some algorithms) for educational purposes and personal use. I tried to implement a column itera

Answer 1

I found a solution to the problem. It's a combination of:

this: Get each nth element of iterator range and this: http://www.codeproject.com/Questions/331444/How-to-use-boost-filter-iterator-as-a-class-member

In the end, there was no way around boost. The solution is very simple and looks like:

 template<class U>
 struct EveryNth {
     bool operator()(const U& ) { return m_count++ % N == 0; }
     EveryNth(std::size_t i) : m_count(0), N(i) {}
 private:
     int m_count;
     std::size_t N;
 };

class Matrix{
// code here

    typedef boost::filter_iterator<EveryNth<T>, 
                               typename std::vector<T>::iterator> FilterIter;

    FilterIter  begin_jump(std::size_t i){
        return boost::make_filter_iterator<EveryNth<T> >(EveryNth<T>(i), data.begin(),      data.end());
    }

    FilterIter end_jump(std::size_t i){
       return boost::make_filter_iterator<EveryNth<T> >(EveryNth<T>(i), data.end(), data.end());
    }

};

and the main:

int main(int argc, char *argv[]){

    std::vector<int> b = {1,2,3,4,5,6,7,8,9};
    MVector<int> a = MVector<int>(b);
    for_each(a.begin_jump(2), a.end_jump(2), 
             [](int i){std::cout << i << " " ;} 
        );

    std::cout << std::endl;
    return 0;
}

bash-3.2$ ./main
1 3 5 7 9 

or using a.begin_jump(3) instead of two:

bash-3.2$ ./main
1 4 7 

which is exactly the intended result.