满足条件时填写nan值

Question

我有一个如下所示的数据框架:

df = pd.DataFrame({'A': [1, np.nan, np.nan, np.nan, 3, 3, 3, 3, np.nan, np.nan, np.nan, 5, 5, 5, 6, 6, 6, np.nan, np.nan, np.nan, 6, 7, 8, 9, 10,np.nan, np.nan, 10, 11]})

我想只在前一个非nan值等于当前的非nan值时填充nan值。

预期输出:

df = pd.DataFrame({'A': [1, np.nan, np.nan, np.nan, 3, 3, 3, 3, np.nan, np.nan, np.nan, 5, 5, 5, 6, 6, 6, np.nan, np.nan, np.nan, 6, 7, 8, 9, 10, np.nan, np.nan,10, 11],'fill_nan': [1, np.nan, np.nan, np.nan, 3, 3, 3, 3, np.nan, np.nan, np.nan, 5, 5, 5, 6, 6, 6, 6, 6, 6, 6, 7, 8, 9, 10, 10, 10,10, 11]})

Answer 1

尝试比较bfillffill:

s = df.ffill()
out = s.where(s.eq(df.bfill()))

输出:

A
0      1.0
1      NaN
2      NaN
3      NaN
4      3.0
5      3.0
6      3.0
7      3.0
8      NaN
9      NaN
10     NaN
11     5.0
12     5.0
13     5.0
14     6.0
15     6.0
16     6.0
17     6.0
18     6.0
19     6.0
20     6.0
21     7.0
22     8.0
23     9.0
24    10.0
25    10.0
26    10.0
27    10.0
28    11.0