get_dummies を逆変換する方法
In [1]: import pandas as pd In [2]: s = pd.Series(['a', 'b', 'a', 'c']) In [3]: s Out[3]: 0 a 1 b 2 a 3 c dtype: object In [4]: dummies = pd.get_dummies(s) In [5]: dummies Out[5]: a b c 0 1 0 0 1 0 1 0 2 1 0 0 3 0 0 1 In [6]: s2 = dummies.idxmax(axis=1) In [7]: s2 Out[7]: 0 a 1 b 2 a 3 c dtype: object In [8]: (s2 == s).all() Out[8]: True