Summary Group Method for Factor Objects

DESCRIPTION:

Group Method defining summary operations on factors and ordered factors.

USAGE:

fun(object, ...) 

DETAILS:

The functions of the Summary group ( sum(), prod(), any(), etc) are those functions that return a single value summarizing their input. This method always produces an error, since all the Summary Group functions require a numerical or logical object as an argument. Indeed, the method exists becauseit is necessary to prevent interpretation of factors or ordered factors as numeric objects. Use codes() if you want a numeric representation of the equivalence relation defined by the factor.