How to set specific Coagulate to number particles?

[Kareltje]

I have been reading this forum a lot lately and learning tons.
Now I am running in to the following problem.

I would like to make an effect in which particles attract each other but limit the number of particles to a specific number.
So coagulate force does a lot of this already but I can't get it to make it such that only 2 particles will attract each other.
I can set it such that a single particle only is attracted to another but not that the other is only attracted to the first.

So I would like a situation in which particle A only attracts particle B and particle B only attracts particle A.
A <--> B
With coagulate you can make it that A only looks at a single particle and attracts B but B can just as easily attract a new particle C, and I still end up with a clump of particles in which I cannot control the total number.
A --> B <--> C

Where should I start looking if I want such a situation?

Thanks for the great forum!

[Tekano]

cool, Ive always liked coagulate force.
the node you are looking for is get neighbouring particles. here is a likely setup where if it is true (less than 1 nearby) it pulls together if it is false it pushes away

for optimising you can set to max search to 2 or 3 in the get neighbours as this node can be quite computationally expensive with lots of particles

[Kareltje]

Thanks!
It sort of works.
I still need to figure out the correct values for the cutoff range and the attraction / rejection forces because now it still sometimes turns into a giant ping pong machine.