如何在pandas中合并两个数据帧来替换nan

Question

我想在熊猫中这样做:

我有2个数据帧,A和B,我想只用B值替换A的NaN.

A                                                
2014-04-17 12:59:00  146.06250  146.0625  145.93750  145.93750
2014-04-17 13:00:00  145.90625  145.9375  145.87500  145.90625
2014-04-17 13:01:00  145.90625       NaN  145.90625        NaN
2014-04-17 13:02:00        NaN       NaN  145.93750  145.96875

B
2014-04-17 12:59:00   146 2/32   146 2/32  145 30/32  145 30/32
2014-04-17 13:00:00  145 29/32  145 30/32  145 28/32  145 29/32
2014-04-17 13:01:00  145 29/32        146  145 29/32        147
2014-04-17 13:02:00        146        146  145 30/32  145 31/32

Result:
2014-04-17 12:59:00  146.06250  146.0625  145.93750  145.93750
2014-04-17 13:00:00  145.90625  145.9375  145.87500  145.90625
2014-04-17 13:01:00  145.90625       146  145.90625        147
2014-04-17 13:02:00        146       146  145.93750  145.96875

Thx提前

Answer 1

正确推广的官方方式是A.combine_first(B).更多信息请参见官方文档.

但是,它使用大型数据库A.fillna(B)(使用25000个元素执行测试)大规模地表现出色:

In[891]: %timeit df.fillna(df2)
1000 loops, best of 3: 333 µs per loop
In[892]: %timeit df.combine_first(df2)
100 loops, best of 3: 2.15 ms per loop
In[894]: (df.fillna(df2) == df.combine_first(df2)).all().all()
Out[890]: True