Cumsum reset at NaN

Question

If I have a pandas.core.series.Series named ts of either 1\'s or NaN\'s like this:

3382   NaN
3381   NaN
...
3369   NaN
3368   NaN
         


        

Answer 1

If you can accept a similar boolean Series b, try

(b.cumsum() - b.cumsum().where(~b).fillna(method='pad').fillna(0)).astype(int)

Starting from your Series ts, either b = (ts == 1) or b = ~ts.isnull().