大熊猫：使用其他两列中的任何一个添加新列

Question

pd.DataFrame({'A':[None,2,None,None,3,4],'B':[1,2,3,4,5,6]})

     A  B
0  NaN  1
1    2  2
2  NaN  3
3  NaN  4
4    3  5
5    4  6

how do I add column C that will take the value from column A if it's not NaN, otherwise column B 's value?

     A  B  C
0  NaN  1  1
1    2  2  2
2  NaN  3  3
3  NaN  4  4
4    3  5  3
5    4  6  4

Answer 1

try combine_first() :

In [184]: a['C'] = a['A'].combine_first(a['B']).astype(int)

In [185]: a
Out[185]:
     A  B  C
0  NaN  1  1
1  2.0  2  2
2  NaN  3  3
3  NaN  4  4
4  3.0  5  3
5  4.0  6  4

Answer 2

you could also try fillna() :

In [26]: a['C'] = a['A'].fillna(a['B'])

In [27]: a
Out[27]:
     A  B  C
0  NaN  1  1
1    2  2  2
2  NaN  3  3
3  NaN  4  4
4    3  5  3
5    4  6  4