[boost] Problem creating mapping from string to vector_expression

Hi, I have been trying to create a mapping from string to ublas::vector_expression. template <class T> boost::unordered_map c; vector<int> v (10); for (unsigned i = 0; i < v.size (); ++ i) v (i) = i; c <int>["first"] = v; I have been getting this error : error: no match for ‘operator=’ (operand types are ‘boost::unordered::unordered_map, std::equal_to, std::allocator > >::mapped_type {aka boost::numeric::ublas::vector_expression<int>}’ and ‘boost::numeric::ublas::vector<int>’) columns <int>["first"] = v; Please help.