The regression model looks now like this

Code:

` lmRob(price ~ ., data = data)`

My problem is modelling variables which are depending on each other.

For example

**floor number**and

**elevator**(is a dummy variable 0 or 1)

If the apartment is at ground floor, the existence of a elevator is irrelevant. But if the floor number is higher, the importance of the existence of the elevator is also higher.

How could I model this in my regression model? Any suggestions?

Thank you!