>>> pd.get_dummies(s1, dummy_na=True)
           a      b    NaN
    0   True  False  False
    1  False   True  False
    2  False  False   True

    >>> df = pd.DataFrame({'A': ['a', 'b', 'a'], 'B': ['b', 'a', 'c'],
    ...                    'C': [1, 2, 3]})

    >>> pd.get_dummies(df, prefix=['col1', 'col2'])
       C  col1_a  col1_b  col2_a  col2_b  col2_c
    0  1    True   False   False    True   False
    1  2   False    True    True   False   False
    2  3    True   False   False   False    True

    >>> pd.get_dummies(pd.Series(list('abcaa')))
           a      b      c
    0   True  False  False
    1  False   True  False
    2  False  False   True
    3   True  False  False
    4   True  False  False

    >>> pd.get_dummies(pd.Series(list('abcaa')), drop_first=True)
           b      c
    0  False  False
    1   True  False
    2  False   True
    3  False  False
    4  False  False

    >>> pd.get_dummies(pd.Series(list('abc')), dtype=float)
         a    b    c
    0  1.0  0.0  0.0
    1  0.0  1.0  0.0
    2  0.0  0.0  1.0
    r