Vu Pham

You can use an if statement with inpointgroup() or i@group_randomPt, or simply assign the group directly using the Group field.

Midphase
I did a whole series on this, you can watch the main one here: https://youtu.be/b4A2Oh2uHsQ [youtu.be]

The Houdini plugin that I talk about still works, provided that you change the code as I also show in one of the other videos.

Alternatively for me, the next best thing (and perhaps the best solution of the bunch) is to export an Alembic to Blender and then use Blender's own extension to send it to AE.

This works less hassle. I used this method: exporting from Houdini as Alembic to Blender, then exporting to an After Effects script with the help of a Python tool from a video guide.
Here’s the video everything works fast and simple, all in under 1 minute.
https://youtu.be/-XJ1_ZN4Qx4 [youtu.be]

there are video tutorials about that

• https://www.youtube.com/watch?v=k_kzaH-WZ1o [www.youtube.com]
  
• free, simple, from a very good instructor https://youtu.be/1Dsld-W2zk0 [youtu.be]
  
• https://www.rebelway.net/math-for-fx/ [www.rebelway.net] (paid)
  
• https://www.udemy.com/course/math-in-houdini-fx-vol-1/? [www.udemy.com] (paid)
  
• https://youtu.be/ScYtNmnyF9A [youtu.be]
  
• basic vector https://www.youtube.com/watch?v=7UB2hPax7Pk [www.youtube.com]