returns a new groupVec object constructed from the arguments,
or an empty one if no arguments are supplied.
Arguments
names
the column names for the object.
The function can be called with no arguments, but if it is called
with any arguments, names must be supplied.
classes
the column classes for the object. If not supplied, it is
initialized as ANY, replicated to the length of names.
columns
the list for column data. If not supplied, it is initialized
to new(class) for each class in classes.
Details
This function creates a new groupVec object, putting
the names (if supplied) into the names slot,
the classes (if supplied) into the classes slot,
and the columns (if supplied) into the columns slot.