How to rotate a vertex group with geometry nodes?

Question

As you can see in the image, it's possible to translate the position of a vertex group of an object with Geometry Nodes thanks to the Selection input of the Set Position node and the Input Attribute Toggle of the Geometry Nodes modifier:

How can I achieve the same with a (not existing) node like Set Rotation? Note that the rest of the mesh is adjusted too like in Set Position, like this:

Unfortunately the Transform Geometry node has no Selection input. I tried several attempts of separating the vertex group geometry and joining it afterwards, but that does not respect the connections between the separated parts (well, which makes sense...). The Rotate Instances node has a Selection input, but that doesn't do anything with vertex groups and gives me a warning I don't understand. The closest I get to can be seen in the right part of the following image, but now I'm left with reconstructing through bridging the two faces, which may be possible (other question) but seems overkill to me.

I feel like I am overlooking something obvious, but how to get a straightforward vertex group only Set Rotation?

Answer 1

The node Transform Geometry changes the transformation of the geometry, but not individual elements. Since you want to change specific points of the geometry here, you would have to use the Set Position node, which however uses Fields (processing multiple elements of a given attribute domain).

The solution could look something like this:

Use Named Attribute to use the vertex group. The node Attribute Statistic gives you the mean position of the points of this vertex group.

With Vector Rotate you rotate the selected points around this center.