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Is there a way to directly map a std::vector<unsigned> to an Eigen::VectorXi in the following fashion?

    std::vector<unsigned> a = {1,2,3,4,5};
    Eigen::VectorXi c = Eigen::VectorXi::Map(a.data(), a.size());

I'd like to skip the following step in between:

    std::vector<int> b(a.begin(),a.end());
EigenGrau
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    The types don't match, so in this case you cannot map the data directly. If you want to put the `unsigned` data into a `VectorXi`, you'll have to convert it, in one way or another, to `int` values. – RHertel Sep 09 '19 at 09:30

1 Answers1

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Your line

Eigen::VectorXi c = Eigen::VectorXi::Map(a.data(), a.size());

doesn't "directly map a std::vector<unsigned> to an Eigen::VectorXi," rather, it copies the data to a new Eigen::VectorXi. If you want to wrap the existing data array with Eigen functionality, you should use something like:

Eigen::Map<Eigen::VectorXi> wrappedData(a.data(), a.size());

You can then use use wrappedData as you would any other VectorXi with the exception of resizing the underlying data (that's still owned by the std::vector). See the documentation for more details.

If you're trying to avoid copying the data to a std::vector<int> then you can use a "custom" matrix type, i.e.

typedef Eigen::Matrix<unsigned int, Eigen::Dynamic, 1> VectorXui;
Eigen::Map<VectorXui> wrappedData(a.data(), a.size());
Avi Ginsburg
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  • I think that the main problem here are the incompatible types `unsigned` and `int` of the `std::vector` and `VectorXi`, respectively. – RHertel Sep 09 '19 at 07:09
  • @RHertel I didn't understand OP that way, but I'll change my answer accordingly. – Avi Ginsburg Sep 09 '19 at 07:19