eigen/doc/snippets/Slicing_arrayexpr.cpp

ArrayXi ind(5); ind<<4,2,5,5,3;
MatrixXi A = MatrixXi::Random(4,6);
cout << "Initial matrix A:\n" << A << "\n\n";
cout << "A(all,ind-1):\n" << A(Eigen::placeholders::all,ind-1) << "\n\n";