How To Reset Cumsum After Change In Sign Of Values?

In [46]: d = np.random.randn(10, 1) * 2 In [47]: df = pd.DataFrame(d.astype(int), columns=['data']) I am trying to create a cumsum column where it should reset after a sign chang

Solution 1:

Create new key to groupby, then do cumsum within each group

New key Create: By using the sign change , if change we add one then it will belong to nest group

df.groupby(df.data.lt(0).astype(int).diff().ne(0).cumsum()).data.cumsum()
Out[798]: 
0   -21   -3213   -34   -45262758   -19   -3
Name: data, dtype: int64