Series.cat.
add_categories
Add new categories.
new_categories will be included at the last/highest place in the categories and will be unused directly after this call.
The new categories to be included.
Whether or not to add the categories inplace or return a copy of this categorical with added categories.
If the new categories include old categories or do not validate as categories
See also
rename_categories
reorder_categories
remove_categories
remove_unused_categories
set_categories