pandas 填充缺失值
示例
In [11]: df = pd.DataFrame([[1, 2, None, 3], [4, None, 5, 6],
[7, 8, 9, 10], [None, None, None, None]])
Out[11]:
0 1 2 3
0 1.0 2.0 NaN 3.0
1 4.0 NaN 5.0 6.0
2 7.0 8.0 9.0 10.0
3 NaN NaN NaN NaN用单个值填充缺失值：
In [12]: df.fillna(0)
Out[12]:
0 1 2 3
0 1.0 2.0 0.0 3.0
1 4.0 0.0 5.0 6.0
2 7.0 8.0 9.0 10.0
3 0.0 0.0 0.0 0.0这将返回一个新的DataFrame。如果要更改原始DataFrame，请使用inplace参数（df.fillna(0,inplace=True)）或将其分配回原始DataFrame（df=df.fillna(0)）。
用先前的值填充缺失的值：
In [13]: df.fillna(method='pad') # this is equivalent to both method='ffill' and .ffill()
Out[13]:
0 1 2 3
0 1.0 2.0 NaN 3.0
1 4.0 2.0 5.0 6.0
2 7.0 8.0 9.0 10.0
3 7.0 8.0 9.0 10.0填写以下内容：
In [14]: df.fillna(method='bfill') # this is equivalent to .bfill()
Out[14]:
0 1 2 3
0 1.0 2.0 5.0 3.0
1 4.0 8.0 5.0 6.0
2 7.0 8.0 9.0 10.0
3 NaN NaN NaN NaN使用另一个DataFrame进行填充：
In [15]: df2 = pd.DataFrame(np.arange(100, 116).reshape(4, 4))
df2
Out[15]:
0 1 2 3
0 100 101 102 103
1 104 105 106 107
2 108 109 110 111
3 112 113 114 115
In [16]: df.fillna(df2) # takes the corresponding cells in df2 to fill df
Out[16]:
0 1 2 3
0 1.0 2.0 102.0 3.0
1 4.0 105.0 5.0 6.0
2 7.0 8.0 9.0 10.0
3 112.0 113.0 114.0 115.0