API/BUG: awkward syntax to add categories to a Categorical · Issue #9927 · pandas-dev/pandas (original) (raw)

In [147]: s = pd.Categorical(list('aabbcd'))

In [148]: s2 = list('aabbcdefg')

In [149]: s
Out[149]: 
[a, a, b, b, c, d]
Categories (4, object): [a, b, c, d]

In [150]: s.add_categories(s.categories.sym_diff(Index(s2)).tolist())
Out[150]: 
[a, a, b, b, c, d]
Categories (7, object): [a, b, c, d, e, f, g]

s.add_categories(s2, take_new=True)