How to find all nodes ids associated to a given boundary id

[mcacace]

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Question

Dear moose team,
Inside an external problem class, I would like to store the ids (global or local does not matter) of all nodes that are located on a given boundary (or a std::vector from the input). This would be done once during initialization (so I should have access to the entire mesh information if I am not mistaken). Then I would use the stored vector of node_ids to tell my external app (which is geometric agnostic) to not modify (or better skip) the current system variables associated to those nodal dofs.
I gave it a try looking at the boundary_info reference, but could not find a proper way for it.
Can anyone help? Thanks a lot in advance,
mauro

[mcacace]

I think I found a working solution (see below) - at least for the tests I did so far. It might not be the most elegant though. Any suggestion on how to improve it would be more than welcome.
Thanks,
mauro

    /// get the collector of the boundary ids from their names
    std::vector<boundary_id_type> nodeset_ids =
        MooseMeshUtils::getBoundaryIDs(_mesh, _excluded_boundaries, false);
    /// get the nodes on existing boundaries
    BoundaryInfo & boundary_info = _mesh.getMesh().get_boundary_info();
    auto bc_nodes = boundary_info.build_node_list();
    /// fill ids accordingly
    for (const auto & t : bc_nodes)
    {
      auto nd_id = std::get<0>(t);
      auto bc_id = std::get<1>(t);
      for (unsigned int i = 0; i < nodeset_ids.size(); ++i)
        if (bc_id == nodeset_ids[i])
          _excluded_node_ids.push_back(nd_id);
    }
    

[GiudGiud]

this looks fine actually.
I'd probably use std::find in the vector rather than a for loop but otherwise this is fine

[mcacace]

Thanks @GiudGiud! I'll close the issue then

[GiudGiud]

Thx. I ll be adding a utility to MeshUtils for this btw, for an unrelated project
EDIT: similar need, but no exclusion list. So wont meet this need