Q:

Is there a direct, fast way to "map" list to MatrixXd?

I am looking for a direct, fast method to convert a list<VectorXd> to MatrixXd. How can I do that?
Map<Eigen::MatrixXd> listV(list<VectorXd>)

Doesn't compile. 
I am also thinking about iterating over the list<VectorXd> and fill in the MatrixXd necessarily, but that could be slow and unnecessary.
Although I agree that this answer is helpful to me in resolving my question, but I don't agree that the parent question is a duplicate for this one. The way to access list and vector can be different, so the question should remain open because the answer is different.

A:

No that's not possible because the elements of the std::list are not sequentially stored in memory. So you'll have to process it one column at once, using Map on the std::vector. So only one loop over the elements of the std::list.

