use stdlib functions with indexing instead of Iterators?

user_3301188 0
Viewed 62

I want to use std::partial_sum on Eigen::VectorXd but I couldn't really find Iterators in Eigen data structures at all. Is there some sort of quick Iterator wrapper that uses classic indexing under the hood? Or what would be a good way to do this instead of re-implementing partial sum with indexing?

eigen indexing iterator c++
2 Answers

You can always get the raw pointer to your data and use it in conjunction with the size.

std::partial_sum(array.data(), array.data() + array.rows() * array.cols(), output.data());

There are 2D iterators available in Eigen though, if you want to iterate over one dimension first and then the other one for each element.

user_22667720

This has been implemented in October 2018, and will be part of the 3.4 release. You can already use them with the trunk version, e.g.,

void foo(Eigen::VectorXd& in_out)
{
    std::partial_sum(in_out.begin(), in_out.end(), in_out.begin());
}

Godbolt demonstration (showing near equivalent code to std::vector): https://godbolt.org/z/bFxcCA

See this (merged) pull request, if you are interested in details: https://bitbucket.org/eigen/eigen/pull-requests/519/

user_68702530
Related