python - Pandas 索引插值填充最后一个数据点之后的缺失值

Question

在列末尾有一个缺少值的数据框，例如:

df = pd.DataFrame({'a':[np.nan,1,2,np.nan,np.nan,5,np.nan,np.nan]}, index=[0,1,2,3,4,5,6,7])

     a
0  NaN
1  1.0
2  2.0
3  NaN
4  NaN
5  5.0
6  NaN
7  NaN

使用“索引”插值方法:

df.interpolate(method='index')

返回数据帧，并向前填充最后一个缺失值:

     a
0  NaN
1  1.0
2  2.0
3  3.0
4  4.0
5  5.0
6  5.0
7  5.0

有没有办法关闭该行为并保留最后缺失的值:

     a
0  NaN
1  1.0
2  2.0
3  3.0
4  4.0
5  5.0
6  NaN
7  NaN

Answer 1

我认为0.23.0+中需要新参数limit_direction，请检查this :

df = df.interpolate(method='index', limit=1, limit_direction='backward')
print (df)
     a
1  1.0
2  2.0
3  3.0
4  4.0
5  5.0
6  NaN
7  NaN

编辑:如果想仅在添加参数limit_area内替换NaN:

df = df.interpolate(method='index',limit_area='inside')
print (df)
     a
0  NaN
1  1.0
2  2.0
3  3.0
4  4.0
5  5.0
6  NaN
7  NaN