python - 用 `ffill`(或任何其他方法)填充 na 值，并递增 1

Question

我有以下 DF，我想填充 NA 值。

我想用递增的值填充它，如下所示:

import pandas as pd

data = [[1,1 ],[1, 1 ], [2, None], [3, None]]

df = pd.DataFrame(data, columns = ['user', 'days_unseen'])

#current behavior of ffill, leaves value the same
df['value']=df['value'].ffill()
print(df)

#desired fill - increments last value by 1
desired_data = [[1,1 ],[1, 1 ], [2, 2], [3, 3]]
desired_df = pd.DataFrame(desired_data, columns = ['user', 'days_unseen'])
print(desired_df)

Answer 1

链条Series.isna与 Series.cumsum用于计数缺失值并通过前向填充缺失值来添加最后一个非缺失值:

df['value'] = df['days_unseen'].isna().cumsum() + df['days_unseen'].ffill()
print(df)
   user  days_unseen  value
0     1          1.0    1.0
1     1          1.0    1.0
2     2          NaN    2.0
3     3          NaN    3.0