`merge` filter does not preserve multi-component data

Describe the bug, what’s wrong, and what you expect:

merge filter does not preserve vectors data.

To Reproduce

Please include a code snippet to reproduce the bug in the block below:

import pyvista
from pyvista import examples
filename = examples.download_cavity(load=False)
reader = pyvista.get_reader(filename)
reader.set_active_time_value(2.5)
mesh = reader.read()
internal_mesh = mesh['internalMesh']
boundary_mesh = mesh['boundary']['movingWall']
# Using vtk==9.1.0, the point_data is mostly the same on both meshes
# Arbitrarily change the boundary mesh
boundary_mesh.point_data["U"] = 10
merged_mesh = internal_mesh.merge(boundary_mesh, main_has_priority=False)
print(internal_mesh.point_data)
print(boundary_mesh.point_data)
print(merged_mesh.point_data)

gives

pyvista DataSetAttributes
Association     : POINT
Active Scalars  : p
Active Vectors  : U
Active Texture  : None
Active Normals  : None
Contains arrays :
    U                       float32  (882, 3)             VECTORS
    p                       float32  (882,)               SCALARS
pyvista DataSetAttributes
Association     : POINT
Active Scalars  : p
Active Vectors  : U
Active Texture  : None
Active Normals  : None
Contains arrays :
    U                       float64  (42,)                VECTORS
    p                       float32  (42,)                SCALARS
pyvista DataSetAttributes
Association     : POINT
Active Scalars  : p
Active Vectors  : None
Active Texture  : None
Active Normals  : None
Contains arrays :
    p                       float32  (882,)               SCALARS

Screenshots N/A

---

System Information: Please run the following code wherever you are experiencing the bug and paste the output below. This report helps us track down bugs and it is critical to addressing your bug:

# Get system info
import pyvista as pv
print(pv.Report())

--------------------------------------------------------------------------------
           pyvista : 0.34.dev0
               vtk : 9.1.0
             numpy : 1.22.2
           imageio : 2.14.1
           appdirs : 1.4.4
            scooby : 0.5.11
        matplotlib : 3.5.1
           IPython : 7.31.1
          colorcet : 3.0.0
           cmocean : 2.0
        ipyvtklink : 0.2.2
        itkwidgets : 0.32.1
              tqdm : 4.62.3
            meshio : 5.3.0

Noted in https://github.com/pyvista/pyvista/discussions/2126

[MatthewFlamm]

I wonder also if we could de-activate the VECTORS data then re-activate later. I’m not sure if it is limited to the active vectors yet.

This doesn’t work, which means that it is multi-component data that doesn’t get copied. This is weird to me.

import pyvista
from pyvista import examples
filename = examples.download_cavity(load=False)
reader = pyvista.get_reader(filename)
reader.set_active_time_value(2.5)
mesh = reader.read()
internal_mesh = mesh['internalMesh']
boundary_mesh = mesh['boundary']['movingWall']
internal_mesh.set_active_vectors(None)
boundary_mesh.set_active_vectors(None)
# Using vtk==9.1.0, the point_data is mostly the same on both meshes
# Arbitrarily change the boundary mesh
boundary_mesh.point_data["U"] = 10
merged_mesh = internal_mesh.merge(boundary_mesh, main_has_priority=False)
print(internal_mesh.point_data)
print(boundary_mesh.point_data)
print(merged_mesh.point_data)

pyvista DataSetAttributes
Association     : POINT
Active Scalars  : p
Active Vectors  : None
Active Texture  : None
Active Normals  : None
Contains arrays :
    U                       float32  (882, 3)
    p                       float32  (882,)               SCALARS
pyvista DataSetAttributes
Association     : POINT
Active Scalars  : p
Active Vectors  : None
Active Texture  : None
Active Normals  : None
Contains arrays :
    U                       float64  (42,)
    p                       float32  (42,)                SCALARS
pyvista DataSetAttributes
Association     : POINT
Active Scalars  : p
Active Vectors  : None
Active Texture  : None
Active Normals  : None
Contains arrays :
    p                       float32  (882,)               SCALARS

[MatthewFlamm]

I wonder also if we could de-activate the VECTORS data then re-activate later. I’m not sure if it is limited to the active vectors yet.

I can see some cases where just copying over data may not be possible. For example, copying over NORMALS may not be correct. I can’t come up with a reason why VECTORS would be affected.