Dummy variable

import pandas as pd
import numpy as np
s = ['a', 'b', np.nan]
df = pd.DataFrame(s)
df
0
0 a
1 b
2 NaN 
df = pd.get_dummies(df[0], dummy_na=True)
df
a b NaN
0 1 0 0
1 0 1 0
2 0 0 1