如何将Eigen :: Matrix映射到std :: vector< Eigen :: vector> ;? [英] how to map a Eigen::Matrix to std::vector<Eigen::vector>?
问题描述
例如,如果我有一个 Eigen :: MatrixXd
,其大小为10列和3行,那么如何将其别名为 std ::?向量
? Eigen :: Vector3d
的10个元素的向量
当我说别名时,我的意思是使用相同的内存块而不进行复制。
E.g., if I have an Eigen::MatrixXd
of size 10 columns and 3 rows, how can I alias that to a std::vector
of 10 elements of Eigen::Vector3d
?
when I say alias I mean using the same memory block without copying.
我知道我可以通过以下方式进行反向映射:
I know that I can do the reversed mapping by something like:
std::vector<Vector3d> v(10);
...
Map<Matrix<double,3,Dynamic> > m(v.data().data(), 3, 10);
但是相反,如果我有Eigen :: Matrix,我试图将其转换为Eigen :: vector,但以下代码行编译失败
but reversely, if I have an Eigen::Matrix, I tried to convert it to a vector of Eigen::vector but the following code line failed compilation
Eigen::Matrix2Xd points;
...
std::vector<Eigen::Vector2d> v_points(points.data()
Eigen::aligned_allocator<Eigen::vector2d>(points_data()))
推荐答案
使用其中所述的自定义分配器可以实现:是否可以初始化
This is possible using a custom allocator as described there: Is it possible to initialize std::vector over already allocated memory?
为此,您必须将其重新解释为 Vector3d *
:
To this end, you'll have to reinterpret it as a Vector3d*
:
Vector3d* buf = reinterpret_cast<Vector3d*>(mat.data());
然后将其传递给您的自定义分配器:
and then pass it to your custom allocator:
std::vector<Vector3d, PreAllocator<Vector3d>> my_vec(10, PreAllocator<Vector3d>(buf, 10));
另一种选择是将其包装在某些视图中,例如 std :: vector
,例如 gsl :: span
:
Another option would be to wrap it within some views alike std::vector
, e.g. gsl::span
:
gsl::span<Vector3d> view(buf,mat.cols());
在两种情况下, mat
对象都必须在 std :: vector
或 span
的整个生命周期内保持生命。
In both cases, the mat
object must stay alive throughout the lifetime of the std::vector
or span
.
出于完整性考虑,您还可以在 std :: vector
:
For completeness, you can also deeply copy it within a std::vector
:
std::vector<Vector3d> v(10);
Matrix<double,3,Dynamic>::Map(v.data().data(),3,10) = mat;
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