Hi there,

I'm trying to write a generic function to get elements at certain 1D indexes
of a Eigen object, the indexes are given by another Eigen object. This is like the Matlab indexing one vector into another. I got it working for concrete types but not quite for the generic case and I've been trying already for quite a while.
Can someone can give me a hand?

The function looks like:

Code: Select all

template<class Derived1, class Derived2>
typename Derived1::PlainObject indexInto(const Eigen::EigenBase<Derived1> &data, const Eigen::EigenBase<Derived2> &index)
{
  typename Derived1::PlainObject result(1, index.size());
  for(int i = 0; i < index.size(); ++i)
    result(i) = data(static_cast<int>(index(i)));
  return result;
}

Thanks,
Martin

you should soon be able to do result = data(index), in the mean time:

typename Derived1::PlainObject result(data.rows(), index.size());
for(int i = 0; i < index.size(); ++i)
result.col(i) = data.col(index(i));
return result;

Oh! great news! I would be using result = data(index) a lot!

About the mean time solution, I still don't get it to work, now I've tried:

Code: Select all

    template<class Derived1, class Derived2>
    typename Derived1::PlainObject indexInto(const Eigen::EigenBase<Derived1> &data, const Eigen::EigenBase<Derived2> &index)
    {
      typename Derived1::PlainObject result(data.rows(), index.size());
      for(int i = 0; i < index.size(); ++i)
          result.col(i) = data.col(index(i));
      return result;
    }


I get a compile error
C2039: 'col' : is not a member of 'Eigen::EigenBase<Derived>' in the line
result.col(i) = data.col(index(i));

Actually, instead of copying the whole column I would like to access data at 1D indexes and put the result in a Vector or 1D Array depending on the data type.

Thanks
Martin

oh, you have to replace EigenBase by DenseBase

Thanks!