Pandas fillna with an incremented value

Question

I have a dataframe with a column of sequential but not adjacent numbers and missing values.

I'd like to use the fillna function to fill in the missing values with an incremented value from the previous non-missing row.

Here's a simplified table:

index  my_counter
0      1
1      2
2      NaN
3      3
4      NaN
5      NaN
6      8

I'd like to fill in my_counter as such:

index  my_counter
0      1
1      2
2      2.1
3      3
4      3.1
5      3.2
6      8

How can I accomplish this task?

Answer 1

IIUC ffill with groupby cumcount

df.my_counter.ffill()+df.groupby(df.my_counter.notnull().cumsum()).cumcount()/10
Out[92]: 
0    1.0
1    2.0
2    2.1
3    3.0
4    3.1
5    3.2
6    8.0
dtype: float64