You may use a functor like:
class comp_with_indirection
{
public:
explicit comp_with_indirection(const std::vector<float>& floats) :
floats(floats)
{}
bool operator() (int lhs, int rhs) const { return floats[lhs] < floats[rhs]; }
private:
const std::vector<float>& floats;
};
And then you may use it like:
int find_median(const std::vector<float>& v_f, std::vector<int> &v_i)
{
assert(!v_i.empty());
assert(v_i.size() <= v_f.size());
const size_t n = v_i.size() / 2;
std::nth_element(v_i.begin(), v_i.begin() + n, v_i.end(), comp_with_indirection(v_f));
return v_i[n];
}
Note: with C++11, you may use lambda instead of named functor class.
int find_median(const std::vector<float>& v_f, std::vector<int> &v_i)
{
assert(!v_i.empty());
assert(v_i.size() <= v_f.size());
const size_t n = v_i.size() / 2;
std::nth_element(
v_i.begin(), v_i.begin() + n, v_i.end(),
[&v_f](int lhs, int rhs) {
return v_f[lhs] < v_f[rhs];
});
return v_i[n];
}