I have a list of rooms. Physically some rooms can be opened up to make a larger room (by removing a dividing wall). The two individual rooms are called  Lab1 and Lab2 but when opened up the name becomes Lab1-Lab2. 

In my list this is recorded as three rooms. I would like each other these rooms to be listed as Lab1-Lab2 so they are summaried correctly.

A reconfigured room always follows this format with a hyphen separating the subrooms. Other rooms exist which cannot be reconfigured and have a single name such as Lab3.

So this is what I think I need;

Lab1=(new field)Lab1-Lab2,

Lab2=Lab1-Lab2

Lab1-Lab2=Lab1-Lab2

Lab3=Lab3

In some instances there may be more than two subrooms but they are always separated by hyphens. In this instance the result would be largest possible configuration. e.g.

Room1, Room2, Room3, Room1-Room2, Room1-Room2-Room3 and Room2-Room3 would all become Room1-Room2-Room3

This sounds like a tall order so I hope it makes sense.

I needed up doing this without a calculation using a relationships and replace

What's in a name? The important thing is for the sub-rooms to have a ParentID field to link them to the "super-room" record in a self-join relationship.