[R] aggregate example : where is the state.region variable?

[Richard M. Heiberger]

> there is
> no factor in the dataset but why there is not one and
> why a call to another dataset is totally opaque.  

The reason is purely historical.  The state dataset is about
10 years older than the data.frame concept.  At the time the
state.* variables were constructed it was not possible to put
numeric data and factor data into the same rectangular structure.