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

Even more pandas-onic way to do it:

v = pd.Series([1., 3., 1., np.nan, 1., 1., 1., 1., np.nan, 1.])
cumsum = v.cumsum().fillna(method='pad')
reset = -cumsum[v.isnull()].diff().fillna(cumsum)
result = v.where(v.notnull(), reset).cumsum()

Contrary to the matlab code, this also works for values different from 1.